新概念英语3中,关于逗号和and的用法,不清楚.请高手赐教

题目

新概念英语3中,关于逗号和and的用法,不清楚.请高手赐教
我在网上看到,一般英语中逗号由来分割句子.如果两个独立的句子用and相连,and前面要加“,”否则算做错误.
可是新概念3“五十便士的麻烦”A crowd of people gathered round him and a lady rubbed his arm with soap and butter,but George was firmly stuck.
这个句子里面,a crowd of people和lady都是独立的主语,也可以单独成句,为什么不在and前面加上逗号呢?
还有“是我,别怕”里面,Suddenly the door of the storeroom was opened and a man entered. 也应该有独立的主谓吧.

答案

以下是用于连接具有相同语法功能并列项时 and 和逗号的使用规则,供参考： 1. and 用来连接具有相同语法功能的两个并列项； 如：A crowd of people gathered round him and a lady rubbed his arm with soap...