As Trees Get Larger and the Number of Leaves Increases

As trees get larger and the number of leaves increases, transpiration rates rise and demand for water increases. How do mature plant stems meet this added demand for water?

A) Cells of the xylem continue to divide and produce more cells that transport water.
B) Vascular cambium continues to divide, and cells of its inner surface differentiate to form additional secondary xylem cells.
C) Cells of secondary phloem adjacent to the vascular cambium differentiate into xylem cells.
D) Cells present in the pith closest to the xylem differentiate into xylem cells.