只能用that作关系代词的情况：

　　1在不定代词anything,nothing,theone,all,much,any,few,little等作先行词指物时

　　Isthereanythingthatyoudon’tunderstand?

　　2先行词有theonly,thevery修饰物时

　　ThisistheonlybookthatIwant.

　　3先行词为形容词最高级时

　　Thiswasthemosttouchingmovieofthisyearthatmadenumerouspeoplecry.

　　4先行词既有人又有物时

　　Forhoursweweretalkingaboutthepeopleandplacesthatinterestedus.

　　5为避免用词的重复

　　Whoisthemanthatismakingaspeechtothestudents?

　　6先行词前有序数词或thelast修饰时

　　Thisisthefirstnovel(that)Ihaveread.

　　Goingtothetheatreisthelastthing(that)Iwanttodo.

　　7关系代词在定语从句中充当表语的成分

　　Heisnotthemanthatheusedtobe.