Experiments on the positive phototropic response of plants ...

[xclash]

Experiments on the positive phototropic response of plants indicate that
A) light destroys auxin.
B) auxin moves down the plant apoplastically.
C) auxin is synthesized in the area where the stem bends.
D) auxin can move to the shady side of the stem.
E) auxin is only of secondary importance in the process.

[clippers!]

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