Which of the following statements best summarizes the acid growth hypothesis in an actively growing shoot?

A) Auxin stimulates proton pumps in the tonoplast to pump hydrogen ions out of the vacuole and allow water to enter.
B) Auxin-activated proton pumps lower the pH of the cell wall, which breaks hydrogen bonds and makes the walls more flexible.
C) Auxins and gibberellins together act as a lubricant to allow cellulose microfibrils to slide past each other.
D) Auxins activate aquaporins that increase turgor pressure in the cells forcing them to expand.