A) When muscles P and Q relax, arm moves down.
B) When muscles P and Q contract, arm moves up.
C) When muscle P contracts and muscle Q relaxes, the arm moves up.
D) When muscle P relaxes and muscle Q contracts, the arm moves up.
Correct Answer: D
Solution :
In the given figure, P and Q represent triceps and biceps respectively. The triceps and biceps act opposite to each other to make the arm move. Both of these muscles cannot contract or relax at the same time. When triceps relax and biceps contract, the arm moves up. When triceps contract and biceps relax, the arm moves down.
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