Mathematics

This problem is about understanding set complements and operations on finite sets of integers. The key insight is to first explicitly list out what $C$ and $D$ contain—they're just integers in specific ranges—then use the definitions of complement and set operations (like union or intersection) relative to the universal set $U = \mathbb{Z}$. Once you see the actual elements, the relationships become clear.

This problem is about understanding set complements and operations on finite sets of integers. The key insight is to first explicitly list out what $C$ and $D$ contain—they're just integers in specific ranges—then use the definitions of complement and set operations (like union or intersection) relative to the universal set $U = \mathbb{Z}$. Once you see the actual elements, the relationships become clear.