---
title: Rivers, lakes and ponds — how Mova does on the tests · Biology
description: Lesson 10 of the biology course of Mova's primary school: 7 of 12 tests right, exam 3 of 4, every question with the options, the student's choice, the right answer and why it chose.
---

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[home](https://md.mova.elamur.ai/free/en/) / [at school](https://md.mova.elamur.ai/free/en/school-run/) / [Biology](https://md.mova.elamur.ai/free/en/school-run/biology/) / 10

# Rivers, lakes and ponds

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**Tests:** 7 of 12 right · **Exam:** 3 of 4 right · **Kind:** ★★★ · **Understood:** 9 of 16 · **Run:** 2026-10-18, commit `f3c23ea72`

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Lesson 10 of the biology course of Mova's primary school, as Mova's small model took its tests: it had read this lesson and the ones before it and learned from their exercises. Each test shows the options in the order the student saw them, its choice, the right answer, the score of every option and why it chose. The lesson itself, sentence by sentence with trees and pragmatics: [the lesson in the corpora](https://md.mova.elamur.ai/free/en/corpora/school/biology/10-rivers-lakes-and-ponds/).

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Every question of this lesson and each of its options parsed by Mova, with trees and pragmatics: [the lesson's questions in the corpora](https://md.mova.elamur.ai/free/en/corpora/questions/biology/10-rivers-lakes-and-ponds/).

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### Test 1 · ★★★ · right ✓ {#t1}

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«piranhas eat a whole cow in like 5 seconds, seen it in a cartoon» What is right?

- **1.** True, but only in the zoo — no support
- **2.** A myth: piranhas have no teeth at all, so they could never bite through a cow's skin — score 6
- **3.** True: they hunt cows every day — no support
- **4.** A myth: they mostly eat insects, fish, worms and plants, and attacks are rare — **← Mova's choice** · **✓ the right answer** · score 14

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**Why:** It took the question to ask which statement is true. It chose option 4 with score 14, against 6 for the next best. Its support: lesson 10, line 4: «Cartoon piranhas turn a cow into a skeleton in seconds; real red-bellied piranhas mostly eat insects, fish, worms and plants, feed in groups mainly for safety,…», reached through the remembered sentence the question matched. What matched: the same action «eat» (+4); the same doer «real bellied piranhas» (+4); the same thing acted on «insects» (+4); the same property (+2). · [the question and its options parsed, with trees and pragmatics](https://md.mova.elamur.ai/free/en/corpora/questions/biology/10-rivers-lakes-and-ponds/t1/)

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### Test 2 · ★★★ · wrong ✗ {#t2}

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«cartoon otter cracking shells on its tummy in the river, cute» Which is right?

- **1.** Only beavers do that — **← Mova's choice** · no support
- **2.** That is a sea otter trick; river otters do not do it — **✓ the right answer** · no support
- **3.** No otter ever uses stones — no support
- **4.** All otters do it, in rivers and in the sea — no support

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**Why:** No option found support in what it remembers, so it guessed: it took the first option shown. · [the question and its options parsed, with trees and pragmatics](https://md.mova.elamur.ai/free/en/corpora/questions/biology/10-rivers-lakes-and-ponds/t2/)

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### Test 3 · ★★★ · wrong ✗ {#t3}

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What would happen to the fish in a lake if ice sank instead of floating?

- **1.** The fish would live on top of the sunken ice — **← Mova's choice** · score 8
- **2.** The lake would freeze from the bottom up, and many fish could not survive — **✓ the right answer** · score 2
- **3.** Nothing, fish like ice — no support
- **4.** The lake would slowly turn into a river and flow away down to the sea — no support

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**Why:** It took the question to ask what happens next. It chose option 1 with score 8, against 2 for the next best. Its support: lesson 10, line 13: «Water is heaviest at about 4 degrees Celsius, so it sinks to the bottom of a lake while colder water and ice float on top, and fish survive under the ice.», reached through what followed the sentence the question matched. What matched: the same action «survive» (+4); the same doer «fish» (+4). The right option, 2, scored 2. · [the question and its options parsed, with trees and pragmatics](https://md.mova.elamur.ai/free/en/corpora/questions/biology/10-rivers-lakes-and-ponds/t3/)

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### Test 4 · ★★★ · wrong ✗ {#t4}

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Count them: four pond skaters and two dragonflies on the pond. How many legs?

- **1.** 24 — **← Mova's choice** · no support
- **2.** 36 — **✓ the right answer** · no support
- **3.** 30 — no support
- **4.** 40 — no support

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**Why:** No option found support in what it remembers, so it guessed: it took the first option shown. · [the question and its options parsed, with trees and pragmatics](https://md.mova.elamur.ai/free/en/corpora/questions/biology/10-rivers-lakes-and-ponds/t4/)

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### Test 5 · ★★★ · wrong ✗ {#t5}

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Count them: three dragonflies zip past. How many wings?

- **1.** 6 — **← Mova's choice** · no support
- **2.** 12 — **✓ the right answer** · no support
- **3.** 18 — no support
- **4.** 9 — no support

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**Why:** No option found support in what it remembers, so it guessed: it took the first option shown. · [the question and its options parsed, with trees and pragmatics](https://md.mova.elamur.ai/free/en/corpora/questions/biology/10-rivers-lakes-and-ponds/t5/)

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### Test 6 · ★★★ · right ✓ {#t6}

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The school pond is going to have goldfish put in it, and great crested newts live there. What is the cleverest worry?

- **1.** Fish eat newt eggs and larvae, so the newts may disappear — **← Mova's choice** · **✓ the right answer** · score 7
- **2.** The goldfish will all be eaten by the hungry newts — no support
- **3.** The newts will turn orange — no support
- **4.** The pond will freeze faster — score 1

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**Why:** It took the question to ask what it is done to. It chose option 1 with score 7, against 1 for the next best. Its support: lesson 10, line 16: «Great crested newts live on land for much of the year, wrap each egg in a folded leaf in a pond in spring, are protected by law in the UK and do best in ponds…», reached through the same lesson line as the sentence the question matched. What matched: the same action «eat» (+2); the same doer «fish» (+2); it fills the role the question asks for (+2); the same thing acted on «eggs» (+1). · [the question and its options parsed, with trees and pragmatics](https://md.mova.elamur.ai/free/en/corpora/questions/biology/10-rivers-lakes-and-ponds/t6/)

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### Test 7 · ★★★ · right ✓ {#t7}

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«shut up, the salmon don't eat anything going up the river? how'd they jump then» Which is the best answer?

- **1.** They eat flies while jumping high out of the water — score 5
- **2.** They take food from fishermen — no support
- **3.** They live on the fat and strength they built up at sea — **← Mova's choice** · **✓ the right answer** · score 8
- **4.** They eat waterfall rocks — score 5

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**Why:** It took the question to ask what something is like. It chose option 3 with score 8, against 5 for the next best. Its support: lesson 10, line 8: «Atlantic salmon grow big at sea, then swim up the river where they hatched to lay their eggs, finding it by smell; they stop eating on the way and live on the…», reached through the same lesson line as the sentence the question matched. What matched: the same action «live» (+3); the same doer «salmon» (+3); the same place «fat» (+2). · [the question and its options parsed, with trees and pragmatics](https://md.mova.elamur.ai/free/en/corpora/questions/biology/10-rivers-lakes-and-ponds/t7/)

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### Test 8 · ★★★ · right ✓ {#t8}

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«beaver's teeth'd get worn down to nothing chewing trees» What is right?

- **1.** They never stop growing, and the iron makes them extra strong — **← Mova's choice** · **✓ the right answer** · score 8
- **2.** Beavers grow new teeth every week — score 6
- **3.** Beavers use their claws, not teeth — no support
- **4.** Yes, old beavers have no teeth left and must eat soft water plants — score 4

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**Why:** It took the question to ask which statement is true. It chose option 1 with score 8, against 6 for the next best. Its support: lesson 6, line 13: «The male narwhal's tusk is a front tooth up to about 3 metres long that grows through its upper lip, and in the Middle Ages such tusks were sold as unicorn hor…», reached through the remembered sentence the question matched. What matched: the same action «grow» (+4); the same doer «front tooth» (+4). · [the question and its options parsed, with trees and pragmatics](https://md.mova.elamur.ai/free/en/corpora/questions/biology/10-rivers-lakes-and-ponds/t8/)

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### Test 9 · ★★★ · right ✓ {#t9}

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«found a newt, gonna take it home to me own pond» What is right in the UK?

- **1.** Great crested newts are protected; you must not move them without a licence — **← Mova's choice** · **✓ the right answer** · no support
- **2.** Only bad if it is winter — no support
- **3.** Fine, as long as you give it a jar — no support
- **4.** Fine, newts like being moved — no support

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**Why:** No option found support in what it remembers, so it guessed: it took the first option shown. · [the question and its options parsed, with trees and pragmatics](https://md.mova.elamur.ai/free/en/corpora/questions/biology/10-rivers-lakes-and-ponds/t9/)

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### Test 10 · ★★★ · wrong ✗ {#t10}

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«dragonfly larva got my tadpole, bloody vicious, kill it» Which is the best answer?

- **1.** It is a pest that should be wiped out — no support
- **2.** It only eats when it is ill or very hungry after a long, cold winter — no support
- **3.** It is a normal pond hunter, part of the pond's food chain — **✓ the right answer** · no support
- **4.** It is a baby fish gone wrong — **← Mova's choice** · score 8

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**Why:** It took the question to ask which statement is true. It chose option 4 with score 8, the only option with support. Its support: lesson 10, line 10: «Dragonfly larvae live underwater for up to several years and catch insects, tadpoles and small fish with a hinged jaw that shoots out, and adult dragonflies ca…», reached through the remembered sentence the question matched. What matched: the same doer «dragonfly larvae» (+4); the same thing acted on «insects» (+4). The right option, 3, found no support in what it remembers. · [the question and its options parsed, with trees and pragmatics](https://md.mova.elamur.ai/free/en/corpora/questions/biology/10-rivers-lakes-and-ponds/t10/)

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### Test 11 · ★★★ · right ✓ {#t11}

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«muddy river after the storm, did someone dump paint in it» Which is the best answer?

- **1.** Rain rushing off the land carries soil and makes the river faster and browner — **← Mova's choice** · **✓ the right answer** · no support
- **2.** Yes, the colour is always pollution — no support
- **3.** Fish turned the water brown — no support
- **4.** The mud rises from the riverbed by itself on rainy days, as the river bed soaks up rain — no support

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**Why:** No option found support in what it remembers, so it guessed: it took the first option shown. · [the question and its options parsed, with trees and pragmatics](https://md.mova.elamur.ai/free/en/corpora/questions/biology/10-rivers-lakes-and-ponds/t11/)

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### Test 12 · ★★★ · right ✓ {#t12}

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«a mussel 100 years old? older than my great-gran» What is right?

- **1.** Freshwater pearl mussels can live over 100 years — **← Mova's choice** · **✓ the right answer** · no support
- **2.** No mussel lives more than a year — no support
- **3.** They live for ever — no support
- **4.** Only sea mussels live that long, never river ones — no support

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**Why:** Nothing it remembers matched the question, so it guessed: it took the first option shown. · [the question and its options parsed, with trees and pragmatics](https://md.mova.elamur.ai/free/en/corpora/questions/biology/10-rivers-lakes-and-ponds/t12/)

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### Exam question 1 · formal language · right ✓ {#e1}

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Which of the following statements most accurately characterises the survival of fish beneath the ice of a frozen lake?

- **1.** Water attains its greatest density at approximately four degrees Celsius, whereby colder water and ice remain at the surface and the water beneath remains liquid — **← Mova's choice** · **✓ the right answer** · score 8
- **2.** The fish freeze entirely and are revived in spring — score 8
- **3.** The fish generate sufficient bodily heat to melt the ice — score 8
- **4.** The fish migrate to the sea prior to the onset of winter — score 8

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**Why:** It took the question to ask who or what does it. It chose option 1 with score 8, tied with another option at 8 (the first shown, or the one claiming less beyond what it knows, wins). Its support: lesson 10, line 3: «Winter does not kill a lake, because water is heaviest at 4 degrees: the coldest water and the ice float on top like a lid, and fish swim on in the liquid wate…», reached through the remembered sentence the question matched. What matched: it fills the role the question asks for (+6); the same doer «coldest water» (+4). Against it: a different action (counts against) (-2). · [the question and its options parsed, with trees and pragmatics](https://md.mova.elamur.ai/free/en/corpora/questions/biology/10-rivers-lakes-and-ponds/e1/)

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### Exam question 2 · formal language · right ✓ {#e2}

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Identify the principal purpose of the dam constructed by the beaver.

- **1.** The creation of a deep pond which protects the entrance to the lodge and does not freeze to the bottom — **← Mova's choice** · **✓ the right answer** · score 8
- **2.** The prevention of passage by other beavers — no support
- **3.** The storage of timber for consumption in summer, when the bark of standing trees has become too hard to digest — no support
- **4.** The capture of fish confined behind the dam — no support

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**Why:** It took the question to ask which statement is true. It chose option 1 with score 8, the only option with support. Its support: lesson 10, line 12: «Beavers fell trees with their teeth and build dams to make deep ponds that protect their lodge and do not freeze to the bottom; their orange front teeth contai…», reached through the remembered sentence the question matched. What matched: the same action «make» (+4); the same thing acted on «deep ponds» (+4). · [the question and its options parsed, with trees and pragmatics](https://md.mova.elamur.ai/free/en/corpora/questions/biology/10-rivers-lakes-and-ponds/e2/)

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### Exam question 3 · formal language · right ✓ {#e3}

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Select the response consistent with the established facts concerning the diet of red-bellied piranhas.

- **1.** Red-bellied piranhas subsist exclusively upon blood — no support
- **2.** Red-bellied piranhas subsist exclusively upon other piranhas — no support
- **3.** Red-bellied piranhas subsist principally upon insects, fish, worms and plants, attacks upon humans being infrequent — **← Mova's choice** · **✓ the right answer** · score 4
- **4.** Red-bellied piranhas subsist principally upon cattle and humans which enter the water, devouring them in a matter of seconds — no support

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**Why:** It took the question to ask which statement is true. It chose option 3 with score 4, the only option with support. Its support: lesson 10, line 4: «Cartoon piranhas turn a cow into a skeleton in seconds; real red-bellied piranhas mostly eat insects, fish, worms and plants, feed in groups mainly for safety,…», reached through the same lesson line as the sentence the question matched. What matched: the same doer «real bellied piranhas» (+3); the same circumstance (+2). Against it: a different action (counts against) (-1). · [the question and its options parsed, with trees and pragmatics](https://md.mova.elamur.ai/free/en/corpora/questions/biology/10-rivers-lakes-and-ponds/e3/)

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### Exam question 4 · formal language · wrong ✗ {#e4}

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Ascertain the aggregate number of legs possessed by five pond skaters and one dragonfly.

- **1.** Twenty-four — **← Mova's choice** · no support
- **2.** Thirty — no support
- **3.** Forty-two — no support
- **4.** Thirty-six — **✓ the right answer** · no support

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**Why:** No option found support in what it remembers, so it guessed: it took the first option shown. · [the question and its options parsed, with trees and pragmatics](https://md.mova.elamur.ai/free/en/corpora/questions/biology/10-rivers-lakes-and-ponds/e4/)

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- ← previous: [9. Coral reefs, rockpools and the seashore](https://md.mova.elamur.ai/free/en/school-run/biology/9-coral-reefs-rockpools-and-the-seashore/)
- next →: [11. Swamps, marshes, mangroves and bogs](https://md.mova.elamur.ai/free/en/school-run/biology/11-swamps-marshes-mangroves-and-bogs/)
- ↑ back to [Biology](https://md.mova.elamur.ai/free/en/school-run/biology/)