Which word in the sentence is a predicate adjective? a ripe melon should be heavy and should have a sweet and pleasant smell. a. heavy b. pleasing c. smell d. sweet

Your answer would be A. Heavy. 
This is because the word "heavy" is in the predicate, is an adjective, and it modifies the subject through the verb. This is the role that a predicate adjective serves. The concept is that a ripe melon is a heavy melon, where "melon" is not part of the predicate.