Which floral whorl is specified by class A genes alone?
That points to B: Sepal. Compared with the other options, Sepal is the one that correctly describes the ABC MODEL concept. The wrong ones are A) Petal; C) Stamen; D) Carpel. 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.