In plants, the purpose of auxins is to
a. cause plant dormancy.
b. regulate abscission.
c. bring about apical dominance.
d. produce phytochrome.

Auxin is used to stimulate plant growth which occurs at the roots and shoots of plants. you must have heard that plant growth is apical therefore it helps for apical dominance. Apical dominance is the phenomenon whereby the main, central stem of the plant is dominant over (i.e., grows more strongly than) other side stems; on a branch the main stem of the branch is further dominant over its own side branchlets that is the shoot has more control over the lateral bud growth.