People all around the world have been doing as much as they can the people in Afghanistan.

问题补充：

People all around the world have been doing as much as they can the people in Afghanistan.

A. help

B. to help

C. helping

D. helped

答案：

A. help

(答案→)B. to help

C. helping

D. helped

解析：句意：全世界的人们尽他们的全力来帮助阿富汗人民。表示目的，故用不定式作目的状语，选B。