When a mouse cell and a human cell are fused, the membrane proteins of the two cells become uniformly distributed over the surface of the hybrid cell. This occurs because
A) proteins are asymmetrically distributed within the membrane.
B) different membranes contain different proteins.
C) all proteins in the plasma membrane come from a membrane other than the human or the mouse.
D) many proteins can move around within the bilayer.
E) all proteins are anchored within the membrane.
