Polymerization types and molecular linkages Steps:

• Polythene forms via addition polymerization of ethene monomers adding without by-products, so 1 = addition.
• Nylon forms via condensation polymerization eliminating small molecules like water, providing the contrasting type.
• Proteins share the amide (-CONH-) linkage with nylon via peptide bonds, so 3 = amide.
• Fats feature ester (-COO-) linkages in triglycerides, matching 4 = ester for the shared bond type. Why A is correct:
• A aligns terms with definitions: addition for chain-growth of alkenes (polythene), condensation for step-growth with by-products (nylon), amide per -NHCO- formula in polyamides/proteins, ester per -COOR- in lipids. Why the others are wrong:
• B provides no terms to fill blanks.
• C swaps ester and amide, mismatching amide linkage definition for proteins/nylon.
• D starts with condensation for polythene, violating addition mechanism for ethene.

Final answer: A