When he looked up he suddenly found himselfby a group of teenagers A. to be surrounded;B

问题补充：

When he looked up, he suddenly found himselfby a group of teenagers,

A. to be surrounded;

B. surrounded;

C. be surrounded;

D. having been surrounded;

答案：

A. to be surrounded;

(答案→)B. surrounded;

C. be surrounded;

D. having been surrounded;

解析：考查过去分词作宾补，此题考查的结构是find sth/sb done,句意：当他抬头的时候，他突然发现他自己被一群青少年包围着。be surrounded by被什么包围，在这里surrounded做宾补。所以选B。