Answer:
A combination of a verb and an adverb or a verb and a preposition, or both, in which the combination has a meaning different from the meaning of the words considered separately : "Catch on " is a phrasal verb meaning of understand.
The correct answer should be reward
Predicate nominative is basically a noun that is used as a predicate instead of a verb and stands next to copulative verbs such as is. In this case, the example says "theophylline is (the) reward" where you can see reward being the predicate nominative.