Like you said the answer is A .
I'm just putting the answer because i need point LOL :D
Depending on the subject, he could go to his text book, online ebook, etc. He could look at his review if he was given one. He could find other books relating to the subject that could potentially help. (Not much to go on, hope this helps c:)
Answer:
Dear Dr. Williams is more formal than Hey Doc.
Heya
the answer is invocation.
invocation is an example which epic convention.
tq