as作连词的用法As there are so many people about,the dogs have to b

as作连词的用法
As there are so many people about,the dogs have to be kept in a special enclosure.为什么这里要用as,不用because,as的用法是什么?as在这里是不是充当一个连词引导原因状语从句,所以这里可以用逗号.是不是只要有as这样的连词就可以用逗号?逗号在什么时候可以连接两个句子?

as的意思=because,as可以引导一个原因状语从句.
也就是说As there are so many people about,the dogs have to be kept in a special enclosure.=Because there are so many people about,the dogs have to be kept in a special enclosure.
逗号是在从句在前时加上,比如:
When I was having lunch,someone knocked at the door.有逗号
Someone knocked at the door when I was having lunch.无逗号
as的用法如下：as可用作连词,引导比较、时间、原因及方式等四种状语从句,应注意的是,引导的比较状语从句往往有省略；引导的时间状语从句一般用一般现在时而不用一般将来时；引导原因状语从句时与“Because”和“since”引导的从句比较起起来语气最弱.
as作介词,意思时“作为”,“以……身份”.例如：He came to China as a tourist five years ago.
而表示像…一样时,like通常作介词用,而介词后面通常接名词,代名词和动名词.
as in Australia“和在澳大利亚一样”.
as……as
AS +adj(原级)+AS
AS +adv(原级)+AS
as soon as 一……就
as soon as possible 尽可能快地
as early as possible 尽可能早的
as carefully as you can 尽可能认真地
as careful as you can 尽可能认真的
1.as是连词,表示“随着”的意义.lives是life的复数,意义是“生活”.

2.as是连词,表示“因为,由于”的意义.wanting是现在分词,表示主动意义,wanting to buy cars=who want to buy cars.
再问： 哦，那因为这里有连词as,后面才可以用逗号是吗？as在这里的用法就跟because相同？
再答： 在这个句子当中，as引导了一个原因状语从句，但as的用法其实有很多。都好这个问题并不是只针对于as或其他制定的词，而是当从句提前的时候（从句就是有里连词的句子），需要加逗号，当从句在后时，就不需要加逗号了。 When I was having lunch,someone knocked at the door.有逗号 Someone knocked at the door when I was having lunch.无逗号 那个，你现在学什么英语，多大了？
再问： 哦，那就是只要是从句，就必须有连词？
再答： 必须的，除非可以省略的，比如宾语从句的that