Something to save our earth. Do you think so?A. can doB. must doC. has to doD. must be do

问题补充：

Something to save our earth. Do you think so?

A. can do

B. must do

C. has to do

D. must be done

答案：

A. can do

B. must do

C. has to do

(答案→)D. must be done

解析：something must be done意为:必须采取措施.