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

Option B. are able to drift about in the plasma membrane.

Explanation:

Membrane phospholipid are having a amphiphilic structure which contains a hydrophilic "head" consisting of a phosphate group and two hydrophobic fatty acid "tails" that are connected to a glycerol molecule.

In contact with water, membrane phospholipid hydrophobic tail avoid interaction with water molecules and allow to drift about in the plasma membrane. the hydrophilic heads line up against each other and forms lipid bi-layer that faces towards water.

The movement of membrane phospholipid forms the fluid mosaic model,in which lipid molecules act as solvent and proteins embedded in it. This allows the proteins and lipid to move across plasma membrane.

Hence, The structural property of membrane phospholipid makes them able to drift about in the plasma membrane