The Glycoproteins Found in the Plasma Membrane Function in What

The glycoproteins found in the plasma membrane function in what capacity?

A) to transport molecules across the membrane
B) establishing the identity of the cell
C) to attach to the cytoskeleton on the interior of the cell and maintain the cell in a position relative to other cells
D) to maintain the membrane's fluidity
E) to catalyze reactions that are crucial to the cell's functioning