Answer:
b
In alphabetical order by author's last name.
Explanation:
'Finally' is the answer the others don't make sense if you try to read them with the rest of the sentence.
The outcome of a poorly written subject line would be that the reader wouldn't understand what he/she was reading about. This would in turn, keep the reader confused the rest of the literature and wouldn't be able to focus.
A. is the answer! Hope that helps!