Cryptochrome is structurally characterized by presence of:
B fits best: Photolyase homology region and C-terminal extension. Keep the cryptochrome basics straight and Photolyase homology region and C-terminal extension stands out as the precise answer. Avoid: A) Single domain only; C) Homeodomain; D) Leucine zipper. 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.