—Heavy smog (雾霾 )in eastern and central China seems to get more and more serious.—I agree.

问题补充：

—Heavy smog (雾霾 )in eastern and central China seems to get more and more serious.

—I agree. Something to deal with it.

A. has done

B. is doing

C. must be done

D. must do

答案：

A. has done

B. is doing

(答案→)C. must be done

D. must do

解析：句意：在中国中东部的雾霾似乎变得越来越严重了。——我也这么想。必须采取措施来解决这个问题。结合语境可知下文主语为动作对象，故用被动语态，选C。