theone用来代替前面特指的单数名词,有时可用that代替(尤其在有后置定语的情况下.

　　that=the+单数可数名词/不可数名词代替前面出现的单数可数名词/不可数名词

　　thebookonthedeskisbetterthan/theoneunderthedesk

　　thepopulatinofchinaislargerthanthatofamerica.

　　that常与介词of一起使用

　　什么时候用theone不用that，比如Isthisfactory()youvisitedlastweek?AthatBwhereCtheoneDinwhich此句中为什么不选A而选C

　　从句中theone与that的区别在定语从句中theone是先行词that是关系代词如thisbookistheonethatyouboughtfotme.that作定从中bought的宾语可以省略就等于thisbookistheoneyouboughtfotmeThisisthebookthatyouboughtforme.变成疑问句的两道题isthisbook-----youboughtforme?AthatBtheone答案是BIsthisthebook-----youboughtforme?AthatBtheone答案是A所以，你说的问句，应该是thisisthefactorythatyouvisitedlastweek，然后把that省略，这里就只能选theone了。