History is ( ) a subject that only lets us know something in history; it also tells us a lot of truth.

A．less than

B．more than

C．no more than

D．not more than

在回采工作面出现下列（）必须停机闭锁处理。

A.机头出现卡大块矸

B.卡大块煤块

C.其它大块物料

D.小木棍