求助 曼哈顿里面的从句引导词没有which 是怎么回事

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曼哈顿78页
Common subordinator markers include
although,before,unless, because, that, so that, if, yet, after while, since, when.
为什么没有which, which 可以引导很多从句 例如宾语从句 等
求NN 解答一下 感谢