The poor boy is in danger. We should do all we help him out.A. can doB. can toC. can to d

问题补充：

The poor boy is in danger. We should do all we help him out.

A. can do

B. can to

C. can to do

D. can

答案：

A. can do

(答案→)B. can to

C. can to do

D. can

解析：这是一个常见结构，补充完整就是：We should do all we can do to help him out。