APETALA2 (AP2) is unique because it is:
That points to C: Non-MADS box gene. Compared with the other options, Non-MADS box gene is the one that correctly describes the ABC MODEL concept. The wrong ones are A) Class B gene; B) Class C gene; D) Only expressed in one whorl. 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.