Given a statement, generate a question such that the answer is contained in that statement.
Example: Neurons deliver electrical impulses to other cells
Example solution: What do neurons deliver to other cells?
Example explanation: The question generated is valid regarding the information in the statement.

Problem: Muscles contracting makes a person's elbow straighten.

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
Solution: What kind of straightens a person's body?