________ there is a snowstorm or some other bad weather, the mail always comes on time.

1. A.
   Because
2. B.
   If
3. C.
   When
4. D.
   Unless

_______ there is a snowstorm or some other bad weather, the mail always comes on time.

A. Because                   B. Unless               C. As                    D. So

_______there is a snowstorm or some other bad weather, the mail always comes on time．

A．Because                B．If                 C．When                     D．Unless