1.what 引导了一个主语从句,在从句中充当desire to do的宾语.在名词性从句当中,缺少主宾表的话,一般都填what.
在杨利伟成功环绕地球飞行后,我们宇航员最想做的事情就是在太空漫步.
2.that引导一个表语从句,is 是系动词,所以that引导的是表语从句.从句中是一个事实,没有疑问在里面,所以用that.
3、That's why后跟结果,That's because 后跟原因.
eg.He didn't catch the bus,that's why he was late.
He was late,that's because he didn't catch the bus.
4、that 这里为一个代词,代指前面的important questions
One of the most important questions 是主语
they had to cinsider 是定语从句,修饰主语
was是系动词 _that__ of public health 是表语