she was able to come made us very happy
如果不加that句子是不是要变成she was able to come to make us very happy?如果作为主语从句come之前是完整主语，因此和made之间就不用加东西。
要改成：It made us very happy (that)she was able to come
也就是说，这句有二种表达 方法：
1、位于句首的表达方式
That she was able to come made us very happy
因为：that引导的主语从句如果位于句首，则that不能省略，去掉that是错误的。
2、位于句末的表达方式
It made us very happy (that)she was able to come
因为：若that引导的主语从句位于句末，而在句首使用了形式主语it，则that可以省略
这种主语从句，只有这二种表达方法。