Answer
d.
Work Step by Step
Phospholipid molecules, when confronted with a liquid environment, will spontaneously form a lipid bilayer. The heads of phospholipids are hydrophilic, meaning they are comfortable with water; the tails of phospholipids are hydrophobic, meaning they do not appreciate water. Therefore, in the presence of water, phospholipids will group themselves so that their tails face each other and their heads facing the outside environment that contacts water. The formation of a protocell is characterized by the development of an outer membrane in this way.
