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

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：考查非谓语动词及定语从句。第一空考查过去分词作宾语补足语，表示“发现自己被包围”；who引导非限定性定语从句，指代先行词teenagers。故选B。