Meaning: 'Reveals' means to make something known or visible, indicating that the collective behavior of animals is shown through their visual displays.

Wrong options:

• hides: The word 'hides' suggests concealment, which contradicts the idea of displaying behavior; it does not fit contextually as it implies the opposite of revealing.
• appeals: 'Appeals' generally means to make a request or attract interest, which does not align with the context of showing behavior; it lacks the direct connection to visual displays.
• promotes: 'Promotes' means to support or encourage something, which does not fit the context of showing or displaying behavior; it does not convey the idea of making something visible.

Correct answer: peculiar

Explanation: The word 'peculiar' is an adjective that describes the display as unusual or distinctive, which fits well in the context of the sentence. It aligns with the idea that the behavior is not typical, thus providing a clear and relevant description.

Meaning: 'Peculiar' means strange or unusual, indicating that the display of collective behavior from fish shoals is not what one would normally expect.

Wrong options:

• usual: 'Usual' implies something that is common or expected, which contradicts the context of the sentence that highlights the uniqueness of the behavior.
• known: 'Known' suggests familiarity or recognition, which does not convey the sense of strangeness or distinctiveness required in this context.
• sick: 'Sick' typically refers to illness or poor health, which is irrelevant in this context and does not describe the nature of the display.

Correct answer: ripe

Explanation: The word 'ripe' is used here as an adjective to describe the fish as being in a state that makes them vulnerable to predators. This fits grammatically and contextually, as it conveys the idea of being ready for predation.

Meaning: 'Ripe' means fully developed or matured, indicating that the fish are in a state that makes them easy targets for predators.

Wrong options:

• rotten: 'Rotten' implies decay or spoilage, which does not fit the context of the fish being vulnerable; it suggests a negative state rather than a readiness for predation.
• wasted: 'Wasted' suggests something that has been squandered or is in poor condition, which does not accurately describe the fish's state in this context.
• given: 'Given' is a past participle that does not appropriately describe the state of the fish; it lacks the necessary connotation of vulnerability.

Correct answer: disturb

Explanation: The word 'disturb' is a verb that fits grammatically and contextually, indicating that the fish are causing a disruption in the water. This aligns with the action they take in response to a threat, making it a suitable choice.

Meaning: 'Disturb' means to interfere with or disrupt, indicating that the fish are creating waves in the water as a defensive behavior.

Wrong options:

• difference: 'Difference' is a noun that does not fit grammatically as it does not convey an action; it does not relate to the behavior of the fish.
• movement: 'Movement' is also a noun and does not serve as a verb in this context; it fails to describe the action taken by the fish.
• knock: 'Knock' implies a striking action, which does not accurately describe the gentle wave-like motion of the fish; it lacks the appropriate context.