Read the dictionary entry. re • frain [ri-freyn]
1. (verb) to resist doing something
2. (noun) the chorus of a musical piece

Which sentence uses refrain as a noun?

The flight attendant requested that the passengers refrain from smoking.
Students should refrain from using their cell phones during the lecture.
Experienced audience members refrain from clapping until the end.
The haunting refrain stayed with the audience long after the show ended.