it 指同一物体.It 指代前面提到的单数名词,相当于the one.: ----Do you want the cup ---Yes ,I want it. ----Do you want the cup ----No,I want the red one. that 通常用来代替前面出现的可数名词不可数名词,主要是用来避免重复.(比较级中只用that) The weather of Guangzhou is hotter than that of Beijing. .that只能代替事物,不能代替人.one可以代替事物,也可以代替人.在口语中it也可以指人 .it可用作无人称代词,指时间,自然现象(天气,气候,明暗等),距离,量度,价值etc.