I must find out why＿＿＿＿so many students made the same mistake.

A．is it that

B．was it which

C．it is what

D．it was that

对柴油机（）的具体要求是：一是燃油颗粒要适当，大小一致；二是燃油能均匀地充满整个燃烧室。

A.燃烧室

B.润滑油润滑

C.燃油雾化

D.压缩比