新概念英语3中，关于逗号和and的用法，不清楚。请高手赐教

Question

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。

Answer 1

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
and
butter.
--
两个分句的语法功能是相同的。
2.
逗号是表达一个完整意思时几个并列项中间除最后一项外的停顿，用以分隔句子结构内的思想或要素;如果一个句子存在两个以上的并列项，前几个要用逗号隔开，而最后一项则需要用
and
连接;
如:A
crowd
of
people
gathered
round
him,
a
lady
rubbed
his
arm
with
soap
and
butter
and
an
old
man
amiled
at
him.
3.
并列项的连接，一般说来逗号和
and
不需要重复使用，但是当其中一个并列项的长度达到一口气念下来气促时，and
前则需要用逗号隔开;
如:A
crowd
of
people
gathered
round
him
，and
a
lady
stood
calmly
and
rubbed
his
arm
with
soap
and
butter
while
the
others
were
looking
at
him
smiling.
4.
有时候，由于句子中起其他作用的逗号影响到句子的层次关系，and
前也需要用逗号隔开;
如:I
did
not
answer,
and
he,
too,
kept
silent.
我没有回答,
(而)他也不作声。
5.
如果并列的分句之间出现其他结构的插入成分，插入成分的前后都需要用逗号隔开，结果也使得连接最后一个并列句的
and
前出现了逗号。
如:A
crowd
of
people
gathered
round
him，as
it
happened,
and
a
lady
rubbed
his
arm
with
soap
and
butter,