If n is an even positive integer, the double factorial notation n!! represents the product of all the even integers from 2 to n. For example:
8!! = 2 \times 4 \times 6 \times 8
What is the units digit of the following sum?
2!! + 4!! + \cdots + 2022!!
Answer Choices
A. 0
B. 2
C. 4
D. 6
E. 8