Light perception by cryptochrome alters conformation of which region?
Go with B — C-terminal extension. Under cryptochrome, this is the standard explanation you’d use in class: it names the real driver or definition, while the rest are nearby but wrong. Not these: A) N-terminal PHR; C) PAS domain; D) DNA-binding domain. When two options sound similar, choose the one that matches the textbook definition most tightly.
Ref: Best CSIR NET Plant Physiology books: Master Unit 6 with Taiz & Zeiger and Salisbury & Ross. Crack Part C experimental questions with top textbooks.