Phototropins are plant photoreceptors sensitive to:
Pick C: Blue light. Thinking through Phototropin+All step by step rules out the lookalikes and leaves Blue light. Skip these: A) Red light; B) Far-red light; D) UV-B light. For hormones and genes, match the molecule or gene to its real role, not a neighboring pathway.
Ref: Best CSIR NET Plant Physiology books: Master Unit 6 with Taiz & Zeiger and Salisbury & Ross. Crack Part C experimental questions with top textbooks.