According to the acid-growth hypothesis, auxin works by________.A. dissolving sieve plates, permitting more rapid transport of nutrients.B. dissolving cell membranes temporarily, permitting cells that were on the verge of dividing divide more rapidly.C. changing the pH within the cell, permitting the electron transport chain to operate more efficiently.D. increasing the activity of proton pumps that lower the pH of cell walls, allowing cells to elongate.