Correct answer is (c) Lipid bilayer enclosing the drug
Easy explanation: It is defined as the vesicle of lipid bilayers enclosing an aqueous compartment. Most commonly phospholipids, sphingolipids, glycolipids are used to prepare liposomes. Their size ranges from 25 to 5000 nm. A large variety of drugs, peptides or proteins including antibodies and viruses and bacteria can be incorporated into liposomes.