To answer this question, read the following sentence:

Dogs and cats filled the animal shelter and the noise they made was incredibly loud.

What is one adjective in this sentence?

A. shelter

B. noise

C. animal

D. they

Dogs and cats filled the animal shelter and the noise they made was incredibly loud.

Considering the underlined phrase, C. animal is the correct answer. Animal is a noun but it has got an adjectival function here; it has been placed before a noun: shelter, so it tells what sort of shelter the speaker is refering to. For example, a bus shelter is the place where passangers wait for the bus. Bus is also a noun functioning as an adjective.

These options are wrong:

A. shelter: This is a noun functioning as a noun.

B. noise: This is a noun functioning as a noun.

D. they: This is a pronoun, so it substitutes for animals.