The nuclear envelope functions as a __________.a. means of localization of the chromosomes within the cell. b. means of sequestering many of the mRNA processing activities from the cytosol. selective barrier, allowing certain substances in or out. c. means of separating nuclear and cytoplasmic constituents. d. selective barrier that separates nuclear and cytoplasmic constituents, localizes chromosomes within the cell, and sequesters many of the mRNA processing activities from the cytosol.