In the fluid mosaic model of membrane structure:
a. proteins form an inner layer between two layers of lipid
b. proteins coat an inner layer of lipids
c. proteins float in a lipid bilayer
d. proteins are covalently bonded to the lipid bilayer
e. all of the above are true

Proteins float in a lipid bilayer

Explanation:

According to the fluid mosaic model of membrane structure, the membranes are made of the bilayer of lipids. Two layers of amphipathic phospholipids make the bilayer structure in which the non-polar tails of phospholipids of two lipid layers make the inner core of the membrane. Their polar heads are oriented towards the inner and outer surface of the membrane.

Membrane proteins float freely in the bilayer or are joined to some intracellular structure of the cell but are never covalently bonded to the membrane lipids. The integral membrane proteins are inserted into the bilayer while the peripheral membrane proteins are not embedded in the lipid bilayer but are located on the inner or outer surface of the membrane. These proteins are usually bound to exposed regions of integral proteins by noncovalent interactions.