A.I. Explanation:

Correct answer: that

Explanation: The word 'that' serves as a relative pronoun, introducing a clause that specifies which signals are being referred to. It fits grammatically as it connects the clause to the noun 'signals' and maintains the flow of the sentence.

Meaning: 'That' is used to refer to a specific thing or idea, in this case, the signals produced by the Central Pattern Generator.

Wrong options:

• them: 'Them' is a pronoun used to refer to previously mentioned objects or people, but it does not introduce a clause and thus does not fit grammatically here.
• those: 'Those' is a demonstrative pronoun that indicates specific items but does not function as a relative pronoun to introduce a clause, making it unsuitable in this context.
• there: 'There' is an adverb indicating a place or existence, which does not relate to the noun 'signals' and does not fit grammatically.

Correct answer: contract

Explanation: The verb 'contract' appropriately describes the action of muscles tightening or shortening, which is the intended meaning in the context of movement. It fits grammatically as it follows the verb 'to' indicating purpose.

Meaning: 'Contract' means to tighten or shorten, particularly in reference to muscles, which is essential for movement like running or walking.

Wrong options:

• constrain: 'Constrain' means to limit or restrict, which does not accurately describe the action of muscles in this context.
• continue: 'Continue' implies ongoing action but does not convey the specific action of muscles needed for movement, making it contextually incorrect.
• contact: 'Contact' refers to touching or meeting, which does not relate to the action of muscles in the context of movement.

Correct answer: pattern

Explanation: The word 'pattern' refers to a repeated or regular arrangement, which is relevant to the sequence of pulses produced by the CPG. It fits grammatically as it serves as a noun that completes the meaning of the sentence.

Meaning: 'Pattern' means a repeated or regular arrangement, in this case, referring to the sequence of pulses that dictate movement.

Wrong options:

• rhyme: 'Rhyme' pertains to similar sounds in poetry and does not relate to the context of movement or signals, making it irrelevant here.
• route: 'Route' refers to a path or course taken, which does not accurately describe the arrangement of pulses in this context.
• path: 'Path' indicates a way or track but lacks the specificity of a regular arrangement that 'pattern' conveys.

Correct answer: modes

Explanation: The word 'modes' refers to different methods or ways of operation, which is appropriate in the context of switching between different types of movement. It fits grammatically as it is a plural noun that aligns with the preceding context.

Meaning: 'Modes' means different methods or ways of doing something, in this case, referring to various types of movement like walking or standing.

Wrong options:

• ways: 'Ways' is a general term for methods but lacks the specificity and technicality that 'modes' provides in this context.
• times: 'Times' refers to specific moments or durations, which does not relate to the types of movement being discussed.
• directions: 'Directions' implies a course or path to follow, which does not accurately describe the different types of movement modes.