Read the sentence.

We're trying to find out whose car is parked in front of our driveway.

How is the form of who or whom used?

object of a preposition

subject

direct object

possessive

The correct answer is: possessive

Explanation:

Whose is the possessive form of the pronoun "who", which means that it is used to mention the thing a person owns (possession). If we break down the sentence, the function of this word will be more clear:

A car is parked in front of a driveway.

This car belongs to someone.

We are trying to find out who has this car as their possession.

"whose" links all this information into a single sentence: We're trying to find out whose car is parked in front of our driveway.

object of preposition