Stop cutting trees, _______ the earth will become worse and worse.

Stop cutting trees, _______ the earth will become worse and worse.

1. A.
   and
2. B.
   then
3. C.
   because
4. D.
   or

Stop cutting trees, _______ the earth will become worse and worse.

A．and              B．then             C．because          D．or

 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