When he looked up he suddenly found himselfby a group of teenagers looked at him anxiously

问题补充：

When he looked up，he suddenly found himselfby a group of teenagers，looked at him anxiously.

A. to be surrounded；which

B. surrounded；who

C. be surrounded；who

D. having been surrounded；which

答案：

A. to be surrounded；which

(答案→)B. surrounded；who

C. be surrounded；who

D. having been surrounded；which

解析：考查分词用法和定语从句。Him与surround构成被动关系，所以使用过去分词。第二空who指代先行词a group of teenagers在句中做主语。句意：当他抬头看的时候，突然发现自己被一群年轻人包围着，这群年轻人焦急地看着他。