Cytokinins delay leaf senescence by:
That points to B: Inhibiting chlorophyll degradation. Compared with the other options, Inhibiting chlorophyll degradation is the one that correctly describes the Cytokinin concept. The wrong ones are A) Promoting ABA; C) Increasing ethylene; D) Reducing photosynthesis. 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.