Membrane phospholipids
a. have hydrophobic heads that face the center of the membrane and are shielded from water.
b. have hydrophilic tails that face outward and are exposed to water.
c. are able to drift about in the plasma membrane.
d. remain fluid because they are tightly packed against one another.

Option-C

Explanation:

The phospholipids are the major constituents of the cell membrane of a cell. The phospholipids contains the glycerol attached to the phosphate group and forms the hydrophilic heads whereas the fatty acid tails from the hydrophobic portion of the membrane.

The hydrophobic head face outwards whereas the tails face inwards.  The structure of the membrane as arranged in bi lipid layer form and in such a way that the membrane molecules can move.  The other molecules present in the membrane like the proteins can drift in the membrane.

Thus, Option-C is correct.

c should be the answer