Strigolactones are transported mainly via:
B fits best: Xylem. Keep the Striglactone basics straight and Xylem stands out as the precise answer. Avoid: A) Phloem; C) Diffusion only; D) Symplast. 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.