Plants growing in a partially dark environment will grow toward ...

[xclash]

Plants growing in a partially dark environment will grow toward light in a response called phototropism. Which of the following statements is true regarding phototropism?
A) It is caused by an electrical signal.
B) One chemical involved is ethylene.
C) Auxin causes a growth increase on one side of the stem.
D) Auxin causes a decrease in growth on the side of the stem exposed to light.
E) Removing the apical meristem enhances phototropism.

[clippers!]

I chose C and got the answer, hope that helps.