After the proteins TIM and PER reach a high level during the day, what causes their level to decrease at night?

A. High levels of the proteins inhibit the genes that produce these proteins.

B. The genes that produce these proteins become less active when temperature drops.

C. Rapid production of the proteins depleted the supply of the amino acids needed to make them.

D. Decreased light stimulation decreases excitatory transmission throughout the nervous system.

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