Which of the following statements best summarizes the acid growth ...

[xclash]

Which of the following statements best summarizes the acid growth hypothesis in an actively growing shoot?
A) Auxin stimulates proton pumps in the plasma membrane and tonoplast.
B) Auxin-activated proton pumps lower the pH of the cell wall, which breaks bonds and makes the walls more flexible
C) Auxins and gibberellins together act as a lubricant to help stretch cellulose microfibrils.
D) Auxins activate aquaporins that increase turgor pressure in the cells.
E) Auxins and gibberellins are transported to the vacuoles to build up turgor pressure.

[clippers!]

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