Coffee differs in taste according to what beans are used and the degree_________ they are roasted.

题目

Coffee differs in taste according to what beans are used and the degree_________ they are roasted.
高一英语题. A.that B.where c.to which d.in that
(答案是C,请说清楚理由.另外,为什么不用A呢?A和C这样的选项我经常分辨不清,请说详细些这种题该怎么做呢?）
不胜感激!

答案

degree的搭配是 to the degree
句子可以看成they are roasted to the degree