the one 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
the book on the desk is better than /the one under the desk
the populatin of china is larger than that of america.
that常与介词of 一起使用