​Endodermis cells of the root secrete a waxy substance on ____.

​Endodermis cells of the root secrete a waxy substance on ____.
A) ​all of their walls
B) ​the walls that lead into the xylem
C) ​the walls adjacent to the phloem only
D) ​walls of the endodermis that touch each other
E) ​their chloroplasts