Hello. This question is incomplete. The full question is:
Choose the sentence in which the non-restrictive phrase appears in bold.
Mattie, whom I've known since preschool, is the only person I know at my new school.
My friend Mattie is the only person I know at my new school.
Mattie is my oldest friend and the only person I know at my new school.
The only person I know at my new school is Mattie—my oldest friend.
Answer:
Mattie, whom I've known since preschool, is the only person I know at my new school.
Step-by-step explanation:
An unrestricted phrase is one that provides additional information to the text or the sentence in which it is inserted, however, this additional information is not necessary for understanding the text and could easily be discarded, without compromising the integrity and coherence of the text. These phrases are usually separated from the rest of the text using commas.
Based on this, we can say that the correct answer to your question is: Mattie, whom I've known since preschool, is the only person I know at my new school.