In active transport,

a. molecules move across the plasma membrane by crossing the lipid bilayer directly, rather than by using a transport protein.
b. the plasma membrane forms a pocket that pinches inward, forming a vesicle that contains material from outside the cell.
c. no energy input is required from the cell.
d. a vesicle inside the cell fuses with the plasma membrane and releases its contents outside the cell.
e. molecules move across the plasma membrane against their concentration gradient.