Question

when flexing the elbow, the triceps is the _____ and the biceps is the _____
prime mover, flexor
antagonist, flexor/prime mover
extensor, antagonist
protagonist, extensor antagonist

Explanation:

When flexing the elbow, the biceps is the prime - mover or flexor muscle that contracts to cause the movement. The triceps is the antagonist muscle that relaxes and lengthens during elbow flexion.

Answer:

B. antagonist, flexor/prime mover