代词包括:人称代词(I,you,he,she ,it,we ,they,you)
物主代词(名词性物主代词:mine,yours,his,hers,its,theirs,yours,ours ;形容词性物主代词:my,your,his ,her,its,their,your,our)
反身代词(myself,yourself,himself,herself,itself,themselves,yourselves,ourselves)
相互代词
指示代词(here,there,this,that,those,these)
疑问代词(what,when,who,how,whom,however,whatever...)
关系代词
不定代词(it)
以上我举例的代词是我们常用的.现在来分析一下你说的问题.
what 问的是"什么".比如这是什么?就应该说:what is this?属于疑问代词.
It是不定代词,可以指代一句话,词组,或者前面出现过的单词.
that就是那个的意思."That is my book."的意思就是:那是我的书.
one是说话双方都知道的意思,指代前面讲到过的某样东西.