从某种程度上来说，出版物发行单位的经营计划能否如期实现，主要取决于（）。
参考答案：出版物结构是否合理
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
采空区必须在开采结束后（）天内全部封闭采区。
A.45
B.50
C.60
