题目内容：

How glad they were to see each other again in Shanghai!
为什么be动词后面可以加to

优质解答

they were so glad to see each other again in shanghai.这句话改成陈述句就是这样的.
they 主语
were 谓语
so glad 表语
to 后面的是 补足语,以补充说明为什么事情而高兴.这可以是to be 结构也可以是 ing 动名词结构.