如果先行词(物)有序数词,最高级,the very 等等修饰时或者先行词既有人又有物时,并且先行词在从句中作主语或者宾语,引导词只能用that。例如:This is the most interesting book that I have ever read.引导词where意思是先行词在在从句作时间状语。