Being old,he stayed at home.Happy and excited,he ran out.为什么

Being old,he stayed at home.
Being old非谓语动词 做原因状语
Happy and excited,he ran out.
Happy and excited是用来修饰,或者说补充说明he的状态

　　从理论上讲，形容词相当于分词的功能，可以附加在句子的前面作原因状语，这种状语相当于一个从句的作用。

　　作为准句子，习惯上往往要由多个音节构成，如：

• Old and retired (= Since he was old and retired), he stayed at home.由于上了年纪而且已经退休，他就呆在家里。

• Happy and excited (= Because he was happy and excited), he ran out.他又快乐又兴奋，于是就跑了出去。

　　在具体使用时，如果音节太少，这种起状语从句的形容词不仅在结构上看上去而且在声音上听起来都显得过于单薄，因此就需要考虑添加系动词的现在分词being弥补这种不足，于是就有了Being old, he stayed at home。