After some time, the tip of a plant that has been forced into a ...

[xclash]

After some time, the tip of a plant that has been forced into a horizontal position grows upward. This phenomenon is related to
A) calcium release from the endoplasmic reticulum of shaded cells.
B) whether the plant is in the northern or southern hemisphere.
C) gibberellin production by stems.
D) auxin production in cells receiving red light.
E) auxin movement toward the lower side of the stem.

[clippers!]

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