If the Per Gene Is Key to Regulating Circadian Rhythms

If the per gene is key to regulating circadian rhythms, we can predict that

A) the per gene acts independently of neurons in the SCN to modulate daily behaviors.
B) the per gene must be a newly evolved mechanism that is not present in more primitive animals.
C) per expression should increase continuously over time if no environmental cues are provided.
D) animals with low per expression, and thus little PER protein production, should not have a circadian rhythm.