Attempts to chemically isolate vernalin have so far been:
Pick C: Unsuccessful. Thinking through VERNALIZATION & FLOWERING step by step rules out the lookalikes and leaves Unsuccessful. Skip these: A) Highly successful; B) Partially successful; D) Conclusive. For hormones and genes, match the molecule or gene to its real role, not a neighboring pathway.
Ref: Best CSIR NET Plant Physiology books: Master Unit 6 with Taiz & Zeiger and Salisbury & Ross. Crack Part C experimental questions with top textbooks.