Evidence for phototropism due to the asymmetric distribution of ...

[xclash]

Evidence for phototropism due to the asymmetric distribution of auxin moving down the stem
A) was first demonstrated in the coleoptiles of monocots.
B) has been found in all monocots and most eudicots.
C) has been shown to involve only IAA stimulation of cell elongation on the dark side of the stem.
D) can be demonstrated with unilateral red light, but not blue light.
E) is now thought by most plant scientists not to involve the shoot tip.

[clippers!]

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