1. Ethnic profiling is practiced throughout the country.
2. Not everyone who is stopped is frisked.
3. Deon Dennis was stopped and searched outside his apartment
building in Harlem.
4. People are threatened with arrest for disorderly conduct if they
object.
MsBittner
Ah ha, someone is attempting to teach you what passive voice is. Each of those passive sentences, in which the verb's action is happening to the subject of the sentence (rather than the subject doing the verb's action), could have an added "by [noun]". That's what your teacher wants you to identify.
So who practices ethnic profiling? Who stops people and sometimes frisks them?