(   ) 1. Most old city walls were ______ down at that time because they were worn ______.

        A. pulled; off         B. pushed; out        C. pushed; off        D. pulled; out

(   ) 2. We should do our best ______ the environment.

        A. protect                     B. to protect          C. protecting          D. protected

(   ) 3. The Great Pyramid is made ______ of two million stones and each stone ______ more than two tons.

        A. from; weighs     B. up; has              C. from; has          D. up; weighs

(   ) 4. This kind of clothes was very popular ______.

        A. in the 1980s      B. in 1980s            C. in the 1980        D. by the 1980