什麼叫as在從句中充當主語或賓語

as引出非限定性定語從句時，代替整個主句，對其進行說明。

但通常用於像as we allaknow， as it is know， as is know to all， as it is， as is said above， as always mentioned above， as is usual， as is often the case， as is reported in the newspaper等句式中。

as在非限定性定語從句中作主語、表語或賓語，且引出的從句位置比較靈活，可位於句首或句末，也可置於主句中間。通常均由逗號將其與主句隔開。as有“正如……， 就像……”之意。

如：

As it known to the United States， Mark Twain is a great American writer.

美國人都知道，馬克?吐溫是一位偉大的美國作家。（as在從句中作主語）

He forgot to bring his pen with him， as was often the case.

他忘了帶筆，這是常事。（as在從句中作主語）

He is absorbed in work， as he often was.

他正在全神貫注地工作，他過去經常這樣。（as在從句中作表語）

Boy as he was， he was chosen king.

他雖是孩子，卻被選為國王。（as在從句中作表語）

as we all know， the earth is round.

眾所周知，地球是圓的。 （as在從句中作賓語）

The two brothers were satisfied with this decision，as was agreed beforehand.

兩兄弟對此決定都滿意，這項決定在事前都已得到他們的同意。(as在從句中作主語)

Taiwan is，as you know，an inseparable part of China.

你知道，臺灣是中國不可分割的一部分。(as在從句中作賓語)