which的用法
which是一个引导非限制性定语从句的代词，用于指示先行词。在定语从句中，which通常放在先行词之后，并且用来修饰先行词。
which用法详解
1. which one(s)：指代先行词中的一个或多个。例如：I want to buy which one(s) of the books.
2. which case(s)：指代先行词的某一特定情况或状态。例如：In which case(s) did you speak to the teacher?
3. which of：指代先行词中的几个中的一个。例如：The table is which of the ones we had in the living room.
4. which they(re)：指代代先行词的复数形式。例如：The children are which they(re) of the two who are studying abroad.
5. which one(s) to：指代在从句中用来引导非限制性定语从句的哪一个或哪些。例如：Which one(s) to buy, we should consider the prices.
6. which they(ll)：指代在从句中用来引导限制性定语从句的哪一个或哪些。例如：Which they(ll) buy, we should consider the prices.
which用法总结
which引导定语从句时，其用法因语境而异。一般来说，which one(s)、which case(s)、which they(re)和which they(ll)的用法比较常见，需要根据具体语境来选择合适的用法。同时，在定语从句中，which的位置也很重要，需要根据先行词在句子中的语境来选择合适的位置。