the Internet brings much profit in it can cause o lot of social problem.A. IfB. WhileC.

问题补充：

the Internet brings much profit in, it can cause o lot of social problem.

A. If

B. While

C. Once

D. When

答案：

A. If

(答案→)B. While

C. Once

D. When

解析：考查连词的辨析。依据句意来突破。从profit和problem发现前后对比转折，故选B