动火许可证的有效期应根据动火级别而确定，二级动火许可证的有效期可为（）天时间。
A、五
B、六
C、三
参考答案：B
When he woke up, he found himself ____ by a group of villagers. [ ]
A. surrounding
B. being surrounded
C. surrounded
D. surround
组合间隙由人体与（）的间隙和人体与（）的间隙组成。
