英语语法Theyovercameallthedifficultiesandfulfilledtheplanthreemonthsaheadoftime,(D)issomethingwehadnotexpected.A.thatB.whatC.itD.which为什么不选B啊?我经常把what和which混淆,这两个应该怎么区别啊?具体

Question

英语语法
They overcame all the difficulties and fulfilled the plan three months ahead of time,( D ) is something we had not expected.
A.that B.what C.it D.which
为什么不选B啊?我经常把what和which混淆,这两个应该怎么区别啊?
具体用法怎样?
类似的题目还有：In some countries,( what ) is called "equality" does not really mean equal rights for all people.
而这题又用了what,

Answer 1

what引导名词性从句,相当与定语从句的all that.all是先行词,that是关系代词.which引导定于从句.名词性从句相当于名次,做了主语叫主语从句,做了表语叫表语从句,做了宾语叫宾语从句,做了同位语做同位语从句.但就是做不了定语.而which引导的定语从句相当于形容词,修饰前面的名词,本题1中which引导上文的那句话.而本题2中what is called equality一起做does not really mean的主语.