Question

17. In saying, "be careful, or you will get lost in the mud," the writer is using:
A. pun.
B. onomatopoeia.
C. climax.
D. simile.
E. metaphor.

Answer 1

A. 
It is indeed a pun. 
The writer's purpose of this may have been to teasingly warn a character. You can easily cancel out the other answer options as well.