The most important thing _____ we should consider is the first idea ____ he has talked about in the speech. [ ]

A. which; that

B. that; which

C. which; which

D. that; that

分为四组，任选一组作答。每题的备选项中，只有1个最符合题意。

为了在煤矿井下安全使用电能，不论是低瓦斯矿井、高瓦斯矿井或有煤(岩)与瓦斯突出的矿井，均须采用( )设备。

A．矿用防爆型

B．矿用一般型

C．矿用电器

D．矿用电气