she boiled milk before she drank the milk.

she （had） boiled milk before she drank the milk.
在喝牛奶前,她先把牛奶煮沸了.
before从句是过去时,主句的动作是发生在它之前的,应该是用过去完成时,要加上助动词had.
再问： 加had这句话就对了嘛
再答： 时态是个最主要的问题，现在把用词再调整一下。 She had boiled the milk before she drank it. 牛奶是特指的，后面用it避免重复。