Concept:When two nouns together describe the same person, the subject is singular and takes a singular verb.
Explanation:"Your friend and mentor" refers to one person who is both a friend and a mentor, so it is a singular subject.
A singular subject requires a singular verb.
"Has finished" is the correct singular present perfect form.
"Have finished" is plural, so it is incorrect.
"Was finished" changes the meaning to the passive voice.
"Is to be finishing" is not the correct tense structure here.
Answer:A. has finished