What is the prepositional phrase in the sentence: "Scrooge puts his key in the door's keyhole."?
In the door's keyhole
Prepositional phrase construction:
Preposition (in this case, the preposition is in), modifiers (sometimes in prepositional phrases, sometimes not), noun/noun phrase/pronoun that acts as the object of the preposition
In the door's keyhole: in is the preposition (it is indicating location), the and door's are modifiers, keyhole is a common noun and is the object of the preposition