text: <unk>  is the process of covalent attachment of poly(ethylene glycol) polymer chains to another molecule, normally a drug or therapeutic protein.<unk>  is routinely achieved by incubation of a reactive derivative of PEG with the target macromolecule.  The covalent attachment of PEG to a drug or therapeutic protein can "mask" the agent from the host's immune system (reduced immunogenicity and antigenicity), increase the hydrodynamic size (size in solution) of the agent which prolongs its circulatory time by reducing renal clearance.<unk>  can also provide water solubility to hydrophobic drugs and proteins.
option_0: PEGylation
option_1: Halogenation
option_2: Carboxylation
option_3: Chemical engineering
option_4: Chemical modification
option_5: Sterilization 
option_6: Electrolysis
option_7: Biological engineering