39. Protein X contains 7 transmembrane domains, with a short N-terminus and a long C-terminus. Following protein synthesis, the N-terminus of the protein faces the lumen (the inside) of endoplasmic reticulum (ER). After protein X is transported to the cell surface via exocytosis, you would expect the C-terminus of the protein X to be (A) extracellular. (B) cytoplasmic. (C) in the lumen ofER. (D) in the lipid bilayer of the plasma membrane.