The answer is C: Personification because the sun is given human-like qualities ("slumber").
It can't be A because a simile compares two things using "like" or "as".
It can't be B because imagery refers to the senses. The sentence isn't very.. descriptive.
It can't be E because nothing is being exaggerated in any way.
I'll be completely honest and say that I haven't learned about synecdoche yet, haha.
