When he looked up，he suddenly found himself________by 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
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B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。