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

井喷失控是井下作业中性质严重、损失巨大的（）。

A、重大事故

B、严重事故

C、特大事故

D、灾难性事故