Polylactic acid forms via condensation as a polyester

Steps:

• Identify polymerization type: Polylactic acid links lactic acid monomers, releasing water, characteristic of condensation polymerization.
• Confirm structure: Repeating units contain ester linkages (-COO-), defining it as a polyester.
• Rule out addition: No unsaturated monomers or chain growth without byproducts, so not addition polymerization.
• Rule out polyamide: Lacks amide linkages (-CONH-), present in polyamides like nylon.

Why C is correct:

• Polylactic acid is synthesized by condensation polymerization of hydroxy acids, forming ester bonds per the general polyester formula -[O-R-COO]-.

Why the others are wrong:

• A: Addition polymerization applies to alkenes, not this step-growth process.
• B: Polyamides require amine and carboxylic acid groups, absent here.
• D: It is a polyester, not a polyamide.

Final answer: C