Answer:
The answer is C. a diol and a dicarboxylic acid
Explanation:
Because Esterification (formation of an ester) is a process that requires an alcohol to react with a carboxylic acid.
Polyester means many ester units.
one alcohol + one carboxylic acid make one ester
thus more than one of each functional groups will make more than on ester unit.
That is why diol (2OH functional groups) + dicarboxylic acid (2 Carboxyl groups) will make polyesters.
