What happens when troponin and tropomyosin block the active sites of actin?

The correct answer is "It prevents spontaneous muscle's contraction".

Explanation:

Muscle contraction is produce by the interaction of actin and myosin filaments. Basically, myosin binds to the active sites of actin, which produces a protein complex (known as actomyosin) that allows that the filaments slide past each other and generate a contraction. When troponin and tropomyosin block the active sites of actin prevents spontaneous muscle's contraction, because a nervous impulse is needed to remove the inhibitors and that myosin starts the contraction.