Question

question 15 in the 1940s, scientists discovered plants grow taller or shorter based on another plant hormone called -- a acid b gibberellin c melatonin 3 points

Explanation:

Gibberellin is a plant - hormone that can promote plant growth, causing plants to grow taller. Acid is a general chemical term not related to plant height regulation in this context. Melatonin is mainly associated with the sleep - wake cycle in animals and not a plant hormone for height regulation.

Answer:

B. Gibberellin