39. In vertebrate photoreceptor cells, which of the following responses occurs when light stimulation is present? (A)The photoreceptor becomes depolarized. (B) The photoreceptor cell releases the neurotransmitter glutamate. (C)The G-protein signaling activity of opsin is shut down in the photoreceptor cell. (D) The cGMP-gated sodium channel on the plasma membrane of the photoreceptor cell closes.