先行词不管是物还是人,都可以用that 做关系词,但是有特殊情况,如下：
习惯上要用that引导的定语从句：
(1)当先行词是指物的all,little,few,much,any,anything,everything,nothing,none,the one时,或先行词被all,little,few,much,any,every,no等修饰时.
eg:I have eaten all the food that is left.我把剩下的所有食物都吃了.
(2)先行词是序数词或最高级形容词时,或者先行词被序数词(包括last,next)、最高级形容词及the only,the very等修饰时.
eg:This is the first film that I have seen since I came here.这是我到这里后所看的第一场电影.
(3)先行词包括人和物时.
eg:They often talk about the people and the things that they are interested in.他们常常谈论那些他们感兴趣的人和事.
(4)当主句是以who或which开头的疑问句时,为了避免重复,多用that引导.如：
Which is the house that caught fire last night?昨晚失火的是那座房子?
例句配解释,应该够清楚了!
