在定语从句中，关系代词 which 和 that 都可指物，一般情况下，可以互换使用。但在下列情况下值得注意： ■只能用that而不能用which的情形 (1) 当先行词为：all, little, few, much, none 及 some-, any-, no-, every- 与 thing 所组成的复合单词时，只能用that。如：http://yingyu.chazidian.com There is nothing that will stop us making progress. 没有事情会阻止我们进步。 (2) 当先行词前面有only, some, any, no, every, little, few, much, all, very等形容词修饰时，只能用that。如： This is the only problem that we can’t work out. 这是我们不能解决的唯一的一个问题。 (3) 当先行词由形容词的最高级或序数词修饰时，只能用that。如： This is the most interesting book that I have ever read. 这是我读过的最有趣的书。 (4) 当先行词同时包括人和物时，只能用that。如： Luxun and his works that we are familiar with are considered great. 人们认为我们所熟识的鲁迅及其作品都很伟大。 (5) 当先行词在定语从句中作表语时，只能用that。如： This is a book that I have been looking for since last week. 这就是那本自上周以来我一直在寻找的书。 (6) 当主句是以 which 开头的特殊疑问句时，只能用 that。如： Which is the picture that you drew yesterday? 你昨天画的那张画是哪一张？ ■只能用which而不能用that的情形 (1) 当非限制性定语从句中的先行词指物时，只能用 which。如： The pencil-case, which I bought last week, is missing. 那个铅笔盒，我上周买的，现在不见了。 (2) 关系代词前面有介词时，只能用which。如： The tree under which we used to take a rest has been cut down. 我们过去常在下面休息的那棵树已砍掉了。 (3) 先行词为代词 that 或 that 所修饰时，只能用 which。如： I don’t take that which is too expensive. 我不要太贵的那一个。