It is implied. Again, this technique only works if 19. The subject of the sentence always does the verb 21. In the case of a linking verb, the subject is joined to the predicate adjective or to the predicate nomitive. In otherwords, the linking verb ties the subject to the predicate adjective or to the predicate nomitive.
Subjects are really easy to find.
The crossing out of the prepositional phrases makes it easier to find the subject and verb. There is more information on grammar. Just go to the Grammar Table of Contents .