If p is a positive integer and q is a negative integer, which of the following is the greatest?

A. $p-q$
B. $q-p$
C. $p+q$
D. $-p-q$
E. More information needed
 

If you liked this question, here is an NRICH task which challenges you to use similar mathematical ideas.

This problem is taken from the UKMT Mathematical Challenges.