2. Cell membranes are asymmetrical. Which of the following is a most likely explanation?
(A) The cell membrane forms a border between one cell and another in tightly packed tissues such as epithelium.
(B) Cell membranes communicate signals from one organism to another.
(C) Cell membrane proteins are determined as the membrane is being packaged in the ER and Golgi.
(D) The inner leaflet and outer leaflet of membrane are predetermined by genes.
(E) Proteins can only span cell membranes if they are hydrophobic.