The correct answer is: D. which
The word “which” is used to refer to a thing or group of things. In this case, the kangaroos are being referred to as a group of things.
The word “whom” is used to refer to a person or group of people. In this case, the kangaroos are not being referred to as people.
The word “whose” is used to refer to something that belongs to a person or group of people. In this case, the kangaroos are not being referred to as people, so the word “whose” cannot be used.
The word “who” is used to refer to a person or group of people. In this case, the kangaroos are not being referred to as people, so the word “who” cannot be used.