In darkness, COP1/SPA1 complex mainly causes:
Degradation of HY5 (B) is correct here. This is core cryptochrome: once you know the definition or pathway step, Degradation of HY5 is the clear fit. The wrong ones are A) Activation of HY5; C) Activation of cryptochrome; D) Inhibition of ubiquitination. 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.