Property of Ex-or is as follows :
$(a \oplus b) \oplus b=a$
i.e. Assume we have a message bit $a$ and we Ex-or it with another message bit b and let's call this new bit c. Now to get the original message bit "a" from "c" , we can ex-or c with "b" again and we'll get "a" back.
So, the same concept is applied in this question and answer will be Option B.
