An adjective clause may modify a (n)

adjective

noun

adverb

Noun.

Explanation:

First we need to remember that adjectives are parts of speech which stand beside a noun and modify it. (for example: big city)

Adjective clause is a type of a dependent clause that consist of a relative pronoun (which connects clause with the word we are describing), subject and a verb - they all together serve as an adjective. So, just like adjectives, they also modifies nouns.

E. g. The cookies that my Grandma bakes are very tasty.