Precursor of ABA (abscisic acid).

Answer: Option B

ABA (abscisic acid) is an important plant hormone that regulates numerous aspects of plant growth, development, and stress responses.
Violaxanthin is the precursor of Abscisic acid. A Whereas Precursor is any substance, mostly enzymes, which on application to an inactive substance converts it to an active one. Hence, violaxanthin activates abscisic acid for its work.