Read the sentence. the college cafeteria, which is free for all full- timefaculty, is a popular and safe environment for students to study. which part of the sentence is nonrestrictive clause? a. the college cafeteria b. which is a free for all full-time faculty c. is a popular and safe environment d. for students to study

The part of the sentence that is the nonrestrictive clause is the following one: "(...) which is free for all full-time faculty".  Nonrestrictive relative clauses contain information that is not essential to understand the meaning of the sentence and therefore can be dropped without altering its meaning. If this test is applied and the sentence is still grammatically correct, then it is a nonrestrictive relative clause. What is more, they are introduced by relative pronouns (which, who, where, when).

The college cafeteria, which is free for all full-time faculty, is a popular and safe environment for students to study.

The college cafeteria is a popular and safe environment for students to study.

since it is asking for her reaction to elnora's trouble at school you can rule out any answers with a positive response (b). then you can rule out (d), this is because it does not show the mother's reaction but the daughter's response. that leaves you with two options (a) and (c), by looking at the options you can rule out (c) because it isn't referring back to elnora's issues at school.