as is known to all ... 的 as 在句中作主语
As we all know... 的 as 在句中作know宾语
as在上面两个句子中 是 关系代词，引导定语从句。
as 还可作连词，引导状语从句，如：
Do it as you like.
He talked as he turned back.
as 还可作介词：作为
He works as a teacher.
还有act as guide 中，应该是act as a guide
as is known to all与as we all know中的as都是关系代词，指代后面的整个句子，也就是说，先行词是前面整个句子，在从句中分别充当主语（因为位于谓语动词is之前）和宾语（因为位于及物动词know之后）。
act as guide中的as是介词，因为这里的guide是名词，as是按照的意思，如果as作“按照”解释时，后面跟的是从句，这时as就是丛书连词了。
