原文:While we cannot predict what the future holds, we do know that the student
has to practice modeling by being given problems from many different
applications "as" is done in this book.
連接詞是用來連接句子的，很明顯的is done in this book不是一個句子(缺少主詞)
但有兩種可能，第一種是主詞被省略；第二種是as是介係詞。
請問各位大大，我這樣分析對嗎? 我想分析as詞性的原因，是因為想要查字典，知道as在
這裡代表什麼意思。

do know [that] is done in this book[that]=to practice....透過有問題的案例來學習，就如書中給予的實例

as (it) is 應該是慣用語，省略了 it ,常見句型如：as is done/ as is usually the case 等等表示“如(這般這般)”, 也只有表示“如”時能省略，不是所有 as it is 的 it 都能省略！參考下面劍橋例句：(conj) as (like)As is often the case with children,...https://goo.gl/btvkSd