Final answer:
A dicarboxylic acid and a dihydroxy alcohol are the monomers that combine to form a polyester, such as Polyethylene terephthalate (PET) through condensation polymerization.
Step-by-step explanation:
The monomers that combine to form a polyester are a dicarboxylic acid and a dihydroxy alcohol. During the process of condensation polymerization, these two functional groups react to eliminate water molecules and form ester linkages in the resulting polyester polymer. The most notable example of a polyester is Polyethylene terephthalate (PET), which is synthesized from terephthalic acid and ethylene glycol.