The correct answer is option (C) covalent motion.
The plasma membrane or the cell membrane is semi-permeable in nature allowing the movement of certain substances only. The movement of substances across the membrane is through the passive transport and the active transport.
Passive transport is the movement of substances across the cell membrane along with their concentration gradient from a region of their higher concentration to a region of their lower concentration without the expenditure of energy. It involves diffusion, osmosis and facilitated diffusion. Active transport is the movement of substances from a region of their lower concentration to their region of higher concentration across the cell membrane, against their concentration gradient involving the expenditure of energy.
Thus, covalent motion is not a method of transport of substances across the cell membrane.