Define the universal set U and its subsets A, B, C, D. U contains positive integers less than or equal to 20. A contains multiples of 2.

Step 1: Define the universal set $U$ and its subsets $A, B, C, D$.
The universal set $U$ consists of positive integers less than or equal to 20.

$$U = \{x \in \mathbb{Z}^+ | x \le 20\} = \{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20\}$$

Subset $A$ contains multiples of 2 in $