This is the house about which I told you.
In the above sentence, the relative pronoun "which" is considered to be the prepositional complement of the preposition "about".
1.) If the relative pronoun "which" is the prepositional complement of the preposition "about", what is the rest of the relative clause "I told you" considered to be?
2.) Why is it possible to use a relative clause as a prepositional complement? If the prepositional complement is a clause, it should normally be a nominal clause.