CONSTANS (CO) gene promotes flowering mainly in:
That points to B: Long day plants. Compared with the other options, Long day plants is the one that correctly describes the VERNALIZATION & FLOWERING concept. The wrong ones are A) Short day plants; C) Day neutral plants; D) Biennials. 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.