在and 后面逗号的作用

题目

在and 后面逗号的作用
the guest had,of course ,realized this from the moment bessie opened the door for them and ,long before the final catastrophe,had had a difficult time trying to conceal their amusement.
请问在这句句中and 后面的逗号是什么作用?为什么要加在and后面呢?还有of course前后为何也要家逗号呢?

答案

,long before the final catastrophe,这段是插入语
and 是连接 had had a difficult …… 这句的
of course 一个道理
He,of course,is a policeman
当然了,他是一个警察