Meaning: 'Strategies' refers to planned methods or techniques used to achieve a specific goal, in this case, finding food.

Wrong options:

• since: The word 'since' is a conjunction that indicates time or causation, which does not fit as it does not serve as a noun in this context.
• required: 'Required' is an adjective that implies necessity, but it does not function as a noun and does not fit the context of describing methods.
• small: 'Small' is an adjective describing size, which does not relate to the concept of methods or techniques in this context.

Correct answer: long

Explanation: The word 'long' fits grammatically as an adjective modifying the noun 'tried,' indicating the duration or extent of the efforts made by biophysicists. It is contextually appropriate as it suggests that they have been engaged in this research for an extended period.

Meaning: 'Long' refers to a significant duration of time, indicating that the biophysicists have been trying to explain these behaviors for a considerable time.

Wrong options:

• distortions: 'Distortions' is a noun that refers to alterations or misrepresentations, which does not fit the context of describing the efforts of biophysicists.
• spoken: 'Spoken' is the past participle of 'speak,' which does not fit grammatically as it does not relate to the action of trying in this context.
• enlarge: 'Enlarge' is a verb that means to make something bigger, which does not fit the context of describing the efforts of biophysicists.

Correct answer: likely

Explanation: The word 'likely' fits grammatically as an adverb modifying the verb 'to turn,' indicating the probability of the amoeba turning left after turning right. It is contextually appropriate as it conveys the idea of likelihood in the behavior of the amoeba.

Meaning: 'Likely' means probable or expected to happen, suggesting that there is a high chance of the amoeba turning left after a right turn.

Wrong options:

• conclusions: 'Conclusions' is a noun that refers to judgments or decisions reached after consideration, which does not fit the context of describing the probability of movement.
• short: 'Short' is an adjective that describes length or duration, which does not relate to the probability of turning in this context.
• natural: 'Natural' is an adjective that describes something inherent or instinctive, which does not fit the context of describing likelihood.

Correct answer: rudimentary

Explanation: The word 'rudimentary' fits grammatically as an adjective describing the noun 'memory,' indicating that the memory is basic or underdeveloped. It is contextually appropriate as it suggests that the memory function of the cells is not advanced.

Meaning: 'Rudimentary' means basic or simple, indicating that the memory capability of the cells is at a fundamental level.

Wrong options:

• bodies: 'Bodies' is a noun that refers to physical structures, which does not fit the context of describing a type of memory.
• often: 'Often' is an adverb that indicates frequency, which does not fit grammatically as it does not describe a type of memory.
• dealt: 'Dealt' is the past tense of 'deal,' which does not fit grammatically or contextually as it does not relate to memory.