Cryptochromes regulate circadian clock primarily through:
C fits best: CRY1 and CRY2. Keep the cryptochrome basics straight and CRY1 and CRY2 stands out as the precise answer. Avoid: A) PHYB interaction; B) COP1 only; D) CRY3 only. Light and flowering items often hinge on which photoreceptor or day-length rule is in play.
Ref: Best CSIR NET Plant Physiology books: Master Unit 6 with Taiz & Zeiger and Salisbury & Ross. Crack Part C experimental questions with top textbooks.