表语从句
构成方式：
若从句为陈述句，直接加that;
若从句为特殊疑问句：直接保留特殊疑问词，后面的句子变成陈述句语序;
若从句为一般疑问句：先把一般疑问句变成陈述句语序，然后在其前加上weather或者if;
eg：China is no longer what she used to be.
The question is who is responsible for what has happened.
