疑问代词which通常用来询问某个事物的具体信息或进行选择。以下是其用法：
1. 指示具体事物
例如：Which book are you reading?
2. 用于后置修饰语
例如：I have seen the movie, which was really good.
3. 用于非限制性定语从句中
例如：I love Italy, which is famous for its art and architecture.
4. 用于出现两个或以上可选项时，进行选择
例如：Which color do you prefer, blue or green?
5. 用于表达疑问而不给出具体选项
例如：Which one is the best restaurant in town?
6. 可用于强调特定事物
例如：This painting, which I found in an antique shop, is worth a lot of money.
总之，which是一个多功能的疑问代词，其常见用法是指示具体事物、用于修饰语、在非限制性定语从句中、进行选择，并表达疑问和强调特定事物的作用。
