Dicoumarol acts as:
B fits best: Anticoagulant. Keep the PLANT SEC METABOLITES basics straight and Anticoagulant stands out as the precise answer. Avoid: A) Antibiotic; C) Pigment; D) Hormone. Light and flowering items often hinge on which photoreceptor or day-length rule is in play.
Ref: Best CSIR NET Plant Physiology books: Master Unit 6 with Taiz & Zeiger and Salisbury & Ross. Crack Part C experimental questions with top textbooks.