det (1)哪一个(些)(used to ask for the alternative from two or more people or things)(作疑问词)： W～tie/shoes should I wear? 我应该戴哪一条领带/穿哪一双鞋? W～Mr Smith do you want to speak to? 您要找哪一位史密斯先生讲话? At～airport/station will I meet him? 我去哪一个机场/火车站接他? Have you decided～team you want to join? 你已经决定参加哪一个队了吗?

(2)这一个(些)(used to provide additional information about the preceding)(fml)(作关系词)：Most people start learning computers，～knowledge is very important today. 许多人开始学习电脑，这一知识在今天非常重要。I spent two years in Britain， during～time I learned English. 我在英国待了两年，在此期间我学习了英语。She said something that she shouldn't have said，for～mistake she apologised. 她说了一些不该说的话，对此她表示了歉意。The education budget has been doubled，in～case we can build a new sound lab. 教育预算增加了一倍，在这种情况下我们可以建一个新的语言实验室。He believes in public ownership，～idea I am quite opposed to. 他信奉公有制，对这一思想我十分反对。

pron(1)哪个(些)人(物)(choice or choices out of a known and limited group)(作疑问词)：W～is your favourite film/do you like best? 你最喜欢哪部电影/哪一个? W～of the boys is yours? 哪个男孩是你的? They resemble each other so much that I can't tell～is～. 他们长得太像了，我分不清谁是谁。Ask him～(of the books) are worth reading/he wants. 问问他哪些(书)值得读/他要哪些(书)? I don't know～to believe. 我不知道应相信哪个。

(2)这一个(些) (used to refer to sth mentioned before)(作关系词)： The Browns live in the house～is opposite to ours. 布朗一家住在我们家对面的房子里。That is the factor (～) we should not neglect/the ceremony (～) we have to go through. 这是一个我们不容忽视的因素/我们必须参加的典礼。The missing file for～they were searching has not been found. 他们正在寻找的那份丢失的资料还没有找到。The football team，～has not been set up very long，plays very well this season. 这支组建不久的足球队在本季赛中踢得十分出色。My father bought me several books，one of～was never to my liking. 我父亲给我买了几本书，其中有一本我根本不喜欢。They have found my lost keys，for～I have to thank them. 他们找到了我丢失的钥匙，对此我十分感谢他们。

【说明】which 和 what 在疑问句中作限定词和代词时，which 用来表示从一定(限定)的数目中选择一个或几个，如：Which(flight) is he taking?(他要乘坐哪一次(航班)?)Which(of the)flowers do you like most?(你最喜欢哪些花?)而 what 则用来表示从非限定数目中选择一个或几个，如：What (flight) is he taking?(他要乘坐什么(航班)?)which 后面可以跟of(见上面第2例)，而 what 则不能;当用于指人时，即使所选择的范围不受限定，也经常使用 which，如： Which/What film stars do you admire most?(你最崇拜哪几位/什么样的电影明星?)

【辨异】which 与that 的区别见THAT。