Explanation
The correct answer is A: 2,4-D.
2,4-D (2,4-dichlorophenoxyacetic acid) is a synthetic herbicide that is widely used to control the growth of broadleaf weeds in agriculture and forestry. It is not a naturally occurring plant hormone.
GA (Gibberellic acid), also known as gibberellin, and IAA (Indole-3-acetic acid) are plant hormones that play important roles in various physiological processes such as cell elongation, seed germination, and fruit development. Gibberellin promotes stem elongation, while IAA promotes cell division and elongation.
Therefore, the correct answer is A: 2,4-D.
