The three ways that the cell membrane helps maintain homeostasis within a cell are:
D. The cell membrane controls the concentration of organic molecules in a cell's cytoplasm.
E. The cell membrane allows water into and out of the cell.
A. The cell membrane protects all of the organelles within the cell from injury.
(Note: While A does provide a protective role, it doesn't directly pertain to the concept of homeostasis as closely as D and E do, which deal specifically with regulating internal conditions. However, if required to select three, A can be included for completeness. The most directly relevant to homeostasis would still be D and E, and a third could be interpreted as A in a broader context.)