Answer:
A. The woman who lives next door is a registered nurse.
Explanation:
An adjective clause, also known as a relative clause, is a phrase that describes the noun in the sentence. It is a type of dependent clause, as it can not make sense all alone.
The sentence that correctly shows the usage of the adjective clause is option A. The adjective phrase/clause in the sentence is <em>who lives next door. </em>The woman (noun) is being described (adjective) with the use of this phrase.
Therefore, option A is correct.