Letting $W$ Stand for the Set of Whole Numbers, I the Set

Multiple Choice

Letting $W$ stand for the set of whole numbers, I the set of integers, $I ^ { + }$ the set of positive integers, and $I ^ { - }$ the set of negative integers, perform the indicated operation.
-Find $\mathrm { I } ^ { + } \cap \mathrm { I } ^ { - }$

A) $\mathrm { I } ^ { - }$
B) $\mathrm { I } ^ { + }$
C) I
D) $\varnothing$