.Charcoal was ______ used in blast furnaces(高炉).

题目

.Charcoal was ______ used in blast furnaces(高炉).
A.the chief fuel B.the chief fuel that
我的问题是为什么不用that啊.不要说是凭语感.要从语法的角度透彻的讲讲吧.最好也讲讲到底什么时候能用that.什么时候不能用.或者可以省略.

答案

选A ,后面的used 是过去分词做定语,用b 的话就变成了定语从句,但是that 后面还要加一个was 和used 构成被动语态,也就是：
...Charcoal was the chief fuel that was used in blast furnaces.