We can use the formula for the union of two sets:
|C U D| = |C| + |D| - |C n D|
where |C| means the number of elements in set C, and so on.
We are given that |C| = 3, |D| = 5, and |C n D| = 2. Substituting these values, we get:
|C U D| = 3 + 5 - 2 = 6
Therefore, the set C U D consists of 6 elements.