无论网站是以何种方式创建，网站必须要有（）。

A.网址

B.域名

C.网址和域名

D.logo

Questions and exercises  are given by the computer, which decides ______ to move the students ahead, review an easier level, ____ give more work on the same level.

A．either, or

B．both, and .

C．whether, or

D．not only, but also