一、as we know是固定短语吗？
①
1、As we know是“正如我们知道”，这个结构通常以as 作为关系代词，引导非限制性定语从句，
2、As we know是定语从句，主句与定语从句的谓语表示的动作如果不是同时发生，时态则不要求一致,所以后面没有什么特定的时态要求.
As we know的用法
1、Let's have your gut reaction to the facts as we know them.
请告诉我们你对我们所了解的这些事实的本能反应。
2、He planned to end the welfare system as we know it.
他计划终止现行的福利制度。
②
众所周知:(saying) as is known to everone
Relative explainations:
as is now well known ;as is well known ;as it is known ;as now well known ;it can be well-known that ;it is a matter of common observation that ;it is known that ;it may be well-known that ;it must be well-known that ;it will be well-known that...
it is common knowledge that ;it is learned that...
Examples:
1、众所周知,他是绝对可靠的.
It is well known that he is completely on the square.
2、众所周知,当一种元素与氧结合时,形成的东西被称为氧化物.
It is well known that the thing formed when an element combines with oxygen is called oxide.
3、这场事故众所周知.
This accident is widely known.
4、众所周知,他是有罪的.
It was apparent to all that he was guilty.
5、新的事实已众所周知,政府被迫承认处理间谍丑事失当.
As new facts became known,the Government was forced to climb down over its handling of the spy scandal.
二、画蛇添足是什么短语？
画蛇时给蛇添上脚。比喻做了多余的事，非但无益，反而不合适。《战国策·齐策二》：“蛇固无足，子安能为之足?” 明·施耐庵《水浒全传》第一百十回：“将军功绩已成，威声大震，可以止矣。今若前进，倘不如意，正如‘画蛇添足’也。”。
并列短语 动宾+动宾=并列
③
画蛇添足是由一个故事引出的成语
④
就是一个事情做好还继续做
三、as the years goby是固定搭配吗？
不是，只是一个时间状语从句。
可以说成：as days go by. 固定搭配的短语大可：as a matter of fact，as a result of，as far as I'm concerned等。
as作为连词，除了引导时间状语从句，表示“当…时候”，还可以引导方式状语从句，表示“象…一样，正如…一样”。
如：as you know，as we expect等。
四、as的用法时态有几种？
①表示“当……时”，可以等同于when和while，引出时间状语从句
I saw him as he walking to me当他走向我时我看到了他
②表示“作为”
As a child，he has nothing much to worry about作为孩子，他没有什么好担忧的
③表示“尽管”，引出让步状语从句
As he was young at that time，he already had much money尽管他那时还很年轻，他已经有许多钱了
④表示“正如”
最经典的一个短语“As an old saying goes”俗话说得好（正如俗话说的那样）