第一句,China is what.这就是主干,what 引导了一个表语从句.
no longer只是来表示程度而已.
第二句,the reason后面的why was sad 是reason的定语,用that引导一个表语从句,来说明reason的内容.
其主干是the reason was that he didn't understand me.
用that引导,是因为所引导的从句中没有缺少任何成分.也就是说主、谓、宾齐全.