Which of the following describes movement of molecules into a cell through active transport?

A. Hydrocarbons dissolve in the lipid bilayer and travel down a concentration gradient.
B. Molecules move through passages in the cell membrane that are created by channel proteins.
C. Pockets in the cell membrane form vesicles around extracellular material during endocytosis.
D. Vesicles carrying large molecules moving downhill fuse with the cell membrane.