Hello,

You need to know photoreceptors do not send AP and instead hyperpolarize when stimulated (this was referenced at the beginning of the passage)- so option 1 is false and we can eliminate choices B and D (as they do not contain option 1). Based on the deficit in the cGMP production seen in the passage when GCAP1 is knocked out, there is no reason to believe it is not necessary for normal recovery. The key word here is *normal*- wild-type phenotype. From this, we can know option 2 is true, making the answer A.

For 42- Many channels on the post-synaptic dendrite need to open simultaneously- causing a large change in voltage. Because one channel is only open in Choice B, it is less likely to be the best answer.

Hope this helps