Answer: (a) Auxin
Explanation: The plant hormones responsible for the activation of lateral buds to grow into new branches is the auxins.
The auxins effect the elongation plants stem, stop the growth of lateral buds thereby maintaining apical dominance. They are formed in the
plants stem, buds, and tips of root. An example of Auxin is the Indole Acetic Acid (IA). The Auxin is a plant hormone produced in the stem tip which effects cell elongation.