在复合顶板条件下发生冒顶事故，绝大部分事故前预兆（）。
A.较强烈
B.不明显
C.比较明显
D.非常明显
参考答案：B
中段回流出入塔温差一般多少合适？大小有何利蔽？
Mr. Crossett ___ his old friend when they met at the railway station.
A．shakes hand with
B．shakes hands with
C．shook hand with
D．shook hands with
