－Our classroom__________ every day.

－So it is. It’s our duty to keep it clean and tidy.

A. cleans              B. is cleaning         C. is cleaned

 It 's our duty to_________people_________too many trees.

A. stop; cutting down          B. prevent,  to cut down

C. keep; cutting down         D. make; cut down

Waste paper shouldn’t _____ everywhere. It’s our duty to keep our classroom clean.

      A. be thrown               B. throw                      C. is thrown

 —It’s our duty to           homeless people in earthquake areas           food and clothes.

—I agree with you. We should do something for them.

A. provide, of               B. provide , with             C. provide , for

 Waste paper shouldn’t _____ everywhere. It’s our duty to keep our classroom clean.

        A. be thrown                B. throw                    C. is thrown