3. An adjective clause may also be used to modify the noun which is used in the predicate complement, as:

In this sentence the clause, which I enjoyed, is an adjective clause modifying the noun book, which is used as the predicate complement with the copulative verb was.

4. An adjective clause may also be used to modify the noun which is used as the object of a preposition, as:

Here the adjective clause, which was late, modifies the noun train, which is the object of the preposition on.

Sometimes it is a little difficult to discover these adjective clauses, for frequently the connecting word is omitted, as for example:

In this sentence, the pronoun whom is omitted; the complete sentence would read: