The primary chromophore regulating cryptochrome activity is:
That points to B: FAD. Compared with the other options, FAD is the one that correctly describes the cryptochrome concept. The wrong ones are A) FMN; C) Riboflavin; D) MTHF. If you’re stuck, eliminate anything that contradicts a basic fact you already know for this topic.
Ref: Best CSIR NET Plant Physiology books: Master Unit 6 with Taiz & Zeiger and Salisbury & Ross. Crack Part C experimental questions with top textbooks.