---
title: The Amazon river: pink dolphins, flooded forest, giant fish and pira… — how Mova does on the tests · Biology
description: Lesson 155 of the biology course of Mova's primary school: 5 of 11 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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# The Amazon river: pink dolphins, flooded forest, giant fish and piranhas

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**Tests:** 5 of 11 right · **Exam:** 3 of 4 right · **Kind:** plain · **Understood:** 10 of 15 · **Run:** 2026-10-18, commit `f3c23ea72`

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Lesson 155 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/155-the-amazon-river/).

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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/155-the-amazon-river/).

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### Test 1 · wrong ✗ {#t1}

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In a cartoon a cow steps into a river and a piranha swarm leaves only bones in seconds. What is true?

- **1.** Piranhas live only in cartoons and films, never in real rivers — **← Mova's choice** · score 2
- **2.** Exactly what happens every day — no support
- **3.** Piranhas eat only cows — score 2
- **4.** The scene is a myth; most piranhas are timid scavengers and people swim among them — **✓ the right answer** · no support

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**Why:** It took the question to ask which statement is true. It chose option 1 with score 2, tied with another option at 2 (the first shown, or the one claiming less beyond what it knows, wins). Its support: lesson 146, line 17: «Chinese water dragons live beside rivers, jump into water when scared and can stay under for around 25 minutes.», reached through the option's own match among the sentences about the question's things. What matched: the same action «live» (+2); the same circumstance (+1). Against it: a different doer (counts against) (-1). The right option, 4, 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/155-the-amazon-river/t1/)

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### Test 2 · right ✓ {#t2}

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«pink dolphin?? no way, dolphins are grey, that's fake» What is right?

- **1.** Right, it is a painted dolphin — no support
- **2.** The boto really exists and turns pinker with age — **← Mova's choice** · **✓ the right answer** · score -3
- **3.** It is a pink fish, not a dolphin — no support
- **4.** Right, pink dolphins live only in zoos where they are fed pink fish — no support

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**Why:** It took the question to ask which statement is true. It chose option 2 with score -3, the only option with support. Its support: lesson 155, line 5: «The boto, or Amazon river dolphin, can turn its head because its neck bones are not joined, and older botos are often the pinkest because scraped skin heals wi…», reached through the remembered sentence the question matched. What matched: the same action «turn» (+1). Against it: the same doer «boto» (-2); a different thing acted on (counts against) (-2). · [the question and its options parsed, with trees and pragmatics](https://md.mova.elamur.ai/free/en/corpora/questions/biology/155-the-amazon-river/t2/)

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### Test 3 · wrong ✗ {#t3}

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A family of 6 giant otters, sorry, 7, stands on the bank. How many legs altogether?

- **1.** 24 — **← Mova's choice** · no support
- **2.** 35 — no support
- **3.** 14 — no support
- **4.** 28 — **✓ 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/155-the-amazon-river/t3/)

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### Test 4 · wrong ✗ {#t4}

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A boto, an arapaima and a giant otter swim past. How many tails?

- **1.** 2 — **← Mova's choice** · no support
- **2.** 3 — **✓ the right answer** · no support
- **3.** 6 — no support
- **4.** 1 — 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/155-the-amazon-river/t4/)

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### Test 5 · right ✓ {#t5}

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What would happen if the floods stopped coming to the Amazon forest?

- **1.** The river would get much deeper — no support
- **2.** More fish would move up to live in the tree tops instead — no support
- **3.** Nothing at all would change — no support
- **4.** Fish could no longer feed on fruit and spread seeds, and many trees and fish would suffer — **← Mova's choice** · **✓ the right answer** · score 0

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**Why:** It took the question to ask what happens next. It chose option 4 with score 0, the only option with support. Its support: lesson 155, line 7: «In the flooded forest fish like the tambaqui eat fallen fruit and nuts and spread the seeds, doing the job birds do on land.», reached through the option's own match among the sentences about the question's things. What matched: the same circumstance (+2). Against it: the same doer «fish» (-1); 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/155-the-amazon-river/t5/)

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### Test 6 · right ✓ {#t6}

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«a fish that breathes air? fish breathe water, mate» What is right?

- **1.** The arapaima must gulp air because warm flood water holds little oxygen — **← Mova's choice** · **✓ the right answer** · score 9
- **2.** Right, it is just showing off — no support
- **3.** It only breathes air on land, when it crawls out of the river to rest — score 5
- **4.** It is a dolphin, not a fish — no support

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**Why:** It took the question to ask which statement is true. It chose option 1 with score 9, against 5 for the next best. Its support: lesson 155, line 8: «The arapaima, one of the biggest freshwater fish in the world, must come up every ten to twenty minutes to breathe air, because warm flood water holds little o…», reached through the same lesson line as the sentence the question matched. What matched: the same action «hold» (+5); the same doer «warm flood water» (+3); the same thing acted on «little oxygen» (+1). · [the question and its options parsed, with trees and pragmatics](https://md.mova.elamur.ai/free/en/corpora/questions/biology/155-the-amazon-river/t6/)

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### Test 7 · right ✓ {#t7}

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«my brother wants to sit on a lily leaf» What can the giant lily Victoria leaf hold?

- **1.** A car — no support
- **2.** A small child's weight, if spread evenly — **← Mova's choice** · **✓ the right answer** · score 3
- **3.** Nothing heavier than a frog, or the leaf sinks — score -1
- **4.** Only water drops — no support

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**Why:** It took the question to ask who or what does it. It chose option 2 with score 3, against -1 for the next best. Its support: lesson 155, line 12: «The giant water lily Victoria has floating leaves up to about three metres across, held up by air-filled ribs and guarded by spines underneath; a big leaf can…», reached through the same lesson line as the sentence the question matched. What matched: the same action «spread» (+3); the same thing acted on «weight» (+2); the same property (+1). Against it: one says «not», the other does not (counts against) (-3). · [the question and its options parsed, with trees and pragmatics](https://md.mova.elamur.ai/free/en/corpora/questions/biology/155-the-amazon-river/t7/)

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### Test 8 · wrong ✗ {#t8}

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A tour guide says «surfers ride the river here». How can that be?

- **1.** The river flows uphill at night — **← Mova's choice** · score 3
- **2.** Boats make the waves — no support
- **3.** It is a joke, because rivers never have any waves — no support
- **4.** The pororoca tidal wave rolls up the river from the sea — **✓ the right answer** · no support

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**Why:** It took the question to ask what something is like. It chose option 1 with score 3, the only option with support. Its support: lesson 155, line 4: «Near the city of Manaus a dark river like tea and a pale river like milky coffee run side by side for kilometres without mixing, because they differ in tempera…», reached through the option's own match among the sentences about the question's things. What matched: the same doer «dark river» (+3). The right option, 4, 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/155-the-amazon-river/t8/)

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### Test 9 · right ✓ {#t9}

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A heap of brown leaves in the mud suddenly swallows a fish. What was it?

- **1.** A matamata turtle — **← Mova's choice** · **✓ the right answer** · no support
- **2.** A piranha — no support
- **3.** A giant otter — no support
- **4.** A boto — 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/155-the-amazon-river/t9/)

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### Test 10 · wrong ✗ {#t10}

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«that black river's dirty, don't swim, it's oil» What is the dark colour really?

- **1.** Oil from deep wells — no support
- **2.** Dissolved stuff from rotting leaves, like tea — **✓ the right answer** · no support
- **3.** Ink squirted by octopuses that swim up the river — **← Mova's choice** · score 4
- **4.** Black paint from a factory — 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 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 option's own match among the sentences about the question's things. What matched: the same thing acted on «river» (+3); the same action «swim up» (+2). Against it: a different doer (counts against) (-1). The right option, 2, 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/155-the-amazon-river/t10/)

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### Test 11 · wrong ✗ {#t11}

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The bullet train's nose was copied from which Amazon diver?

- **1.** An arapaima's scales — **← Mova's choice** · no support
- **2.** A piranha's sharp teeth — no support
- **3.** A kingfisher's beak — **✓ the right answer** · no support
- **4.** A river dolphin's snout — 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/155-the-amazon-river/t11/)

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

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Select the response consistent with the established facts concerning the piranhas of the Amazon.

- **1.** The majority are timid shoaling fish, frequently scavenging, and are seldom dangerous to swimmers — **← Mova's choice** · **✓ the right answer** · score 6
- **2.** They are entirely without teeth — score 2
- **3.** Shoals habitually reduce whole cattle to skeletons within seconds whenever they enter the water — score 2
- **4.** They subsist exclusively upon the flesh of mammals — no support

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**Why:** It took the question to ask which statement is true. It chose option 1 with score 6, against 2 for the next best. Its support: lesson 155, line 3: «Cartoons show piranhas stripping a cow to bones in seconds; real piranhas are mostly timid shoaling fish and scavengers, and local children swim in piranha riv…», reached through the same lesson line as the sentence the question matched. What matched: the same action «shoal» (+5); the same thing acted on «fish» (+1). · [the question and its options parsed, with trees and pragmatics](https://md.mova.elamur.ai/free/en/corpora/questions/biology/155-the-amazon-river/e1/)

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

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Identify the principal reason for which the arapaima rises periodically to the surface.

- **1.** It thereby feeds upon insects alighting upon the surface of the water during the night — score 0
- **2.** It is obliged to breathe air, the warm flood water holding little oxygen — **← Mova's choice** · **✓ the right answer** · score 9
- **3.** It thereby signals to other members of its species — no support
- **4.** It thereby lowers its body temperature — no support

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**Why:** It took the question to ask which statement is true. It chose option 2 with score 9, against 0 for the next best. Its support: lesson 155, line 8: «The arapaima, one of the biggest freshwater fish in the world, must come up every ten to twenty minutes to breathe air, because warm flood water holds little o…», reached through the same lesson line as the sentence the question matched. What matched: the same action «hold» (+5); the same doer «warm flood water» (+3); the same thing acted on «little oxygen» (+1). · [the question and its options parsed, with trees and pragmatics](https://md.mova.elamur.ai/free/en/corpora/questions/biology/155-the-amazon-river/e2/)

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### Exam question 3 · formal language · wrong ✗ {#e3}

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Which of the following statements most accurately characterises the pororoca?

- **1.** A shoal of predatory fish — **← Mova's choice** · no support
- **2.** A tidal wave advancing up the mouth of the river against its current — **✓ the right answer** · no support
- **3.** A species of freshwater dolphin of a pink colour — no support
- **4.** A tract of seasonally flooded forest — 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/155-the-amazon-river/e3/)

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### Exam question 4 · formal language · right ✓ {#e4}

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Ascertain the reason for which the Rio Negro and the Solimões flow alongside one another for several kilometres prior to mixing.

- **1.** The two waters differ in temperature, velocity and dissolved substances — **← Mova's choice** · **✓ the right answer** · score 3
- **2.** The fish of each river prevent intermingling — no support
- **3.** The one river flows in the contrary direction to the other, so that they cannot join — score 3
- **4.** A submerged wall separates the two channels — no support

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**Why:** It took the question to ask which statement is true. It chose option 1 with score 3, tied with another option at 3 (the first shown, or the one claiming less beyond what it knows, wins). Its support: lesson 155, line 4: «Near the city of Manaus a dark river like tea and a pale river like milky coffee run side by side for kilometres without mixing, because they differ in tempera…», reached through a sentence linked to the one the question matched. What matched: the same action «differ» (+2); the same place «temperature» (+2). Against it: a different doer (counts against) (-1). · [the question and its options parsed, with trees and pragmatics](https://md.mova.elamur.ai/free/en/corpora/questions/biology/155-the-amazon-river/e4/)

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- ← previous: [154. More animal myths: red rags, camel humps, porcup…](https://md.mova.elamur.ai/free/en/school-run/biology/154-more-animal-myths-from-cartoons/)
- next →: [156. The Amazon canopy: howlers, harpy eagles, toucan…](https://md.mova.elamur.ai/free/en/school-run/biology/156-the-amazon-canopy/)
- ↑ back to [Biology](https://md.mova.elamur.ai/free/en/school-run/biology/)