Well, it isn't A because there should only be a period at the end of P.M. It isn't C because it has to be a period between M and D.
So, the answer has to be B.
Hope this helps!
Answer:
to prevent the writer from making grammatical errors
to assist the writer in narrowing his or her topic
to aid the writer in revising his or her essay for unity
to help the writer elaborate on statements
C. I will listen to you, especially in one year or term.
