TASK DEFINITION: In this task, you are given a question and an answer, you would be asked to create the sentence based on the Question-Answer provided. It should be contained within the Question-Answer provided.
PROBLEM: Question: What do muscles need to contract? Answer: stimulus

SOLUTION: Muscles need stimulus to contract.

PROBLEM: Question: Expansion of a gas into a vacuum is irreversible because the external pressure is measurably less than the internal pressure of the gas, and no states of what exist? Answer: equilibrium

SOLUTION: Expansion of a gas into a vacuum is irreversible because the external pressure is measurably less than the internal pressure of the gas, and no states of equilibrium exist.

PROBLEM: Question: Variation in muscle cells gives further insight into some benefits of what type of respiration? Answer: anaerobic

SOLUTION:
Variation in muscle cells gives further insight into some benefits of anaerobic type of respiration.