Hello. This question is incomplete. The full question is:
What is the purpose of the underlined part of the sentence? Everyone who had seen the performance agreed that the actors had done a terrific job.
It is a noun phrase that means the same as everyone.
It is a noun clause acting as the object of agreed.
It is an adverbial phrase modifying agreed.
It is a relative clause modifying everyone.
Answer:
It is a noun phrase that means the same as everyone.
Step-by-step explanation:
The underline phrase represents a noun phrase, where it presents itself as a nucleus of the subject "everyone", assuming its meaning and expanding its meaning. In a simplified way, we can say that a noun phrase is the word in a sentence that performs the same grammatical function as the noun, which in the case of the sentence above is also the subject of the sentence, allowing "everyone" and "who had seem" to present the same meaning.