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, $8!! = 2·4·6·8$. What is the units digit of the following sum?  $2!! + 4!! + 6!! + · · · + 2018!! + 2020!! + 2022!!$ 
选项为:A:$$0$$  B:$$2$$  C:$$4$$  D:$$6$$  E:$$8$$  请回答其中一个选项.