Phytochrome exists in two interconvertible forms known as:
Pr and Pfr (B) is correct here. This is core PHOTOPERIODISM: once you know the definition or pathway step, Pr and Pfr is the clear fit. The wrong ones are A) P680 and P700; C) PSI and PSII; D) FAD and FMN. If the topic is about gradients or potentials, water/solutes move from higher to lower of the relevant quantity.
Ref: Best CSIR NET Plant Physiology books: Master Unit 6 with Taiz & Zeiger and Salisbury & Ross. Crack Part C experimental questions with top textbooks.