Exercise

We know that this is so, but all too often we recognize this truth only in our backward glance when we remember what it was and then suddenly realize that it is no more.

people think of cowboys as free people, unafraid to battle with wild animals, living close to nature, with the trees and the sky and the stars.

Clearly , science may involve not only careful observation but also a willingness to be creative; this may entail looking beyond existing paradigms governing research in a given area of study.

要點分析和參考譯文

要點：此句又兩個并列結構存在，一個使全局的主干結構，即由but連接的兩個分句"we know……，but all too often we recognize……"；另一個是glance 后面跟著由and連接的兩個并列的狀語從句。這兩個狀語從句在實踐上存在著先后順序，在結構上是一個對偶句，而且第二個狀語從句得主語省略，即when we remember what it was and then suddenly (we) realize that it is no more。
參考譯文：我們大家都知道這是實際情況。可我們卻常常只是再回首往事想起它當時的情景時才認識到，并且此時我們會突然發現它已不復存在了。

要點：句中謂語動詞為一短語"think of …… as", 后接名詞短語" free people"及形容詞短語"unafraid to battle with wild animals"并列作cowboys的賓語補足語。分詞短語"living……"及介詞短語"with the trees……" 做伴隨及方式狀語。
參考譯文：人們把牛仔看成是自由自在的人，毫不懼怕與野獸搏斗，在大自然的懷抱中生活，與樹木，天空及星斗共存。

要點：此句是由;號鏈接在一起的兩個獨立的句子，是一個并列的結構。第二個分句的主語this 指的應該是前面的整個句子的含義，否則會出現理解上的偏差。Existing paradigms 是介詞beyond 的賓語，而governing research 是paradigms的定語。
參考譯文：可見，科學包括的不僅是仔細觀察，而且還包括樂于去創新，這就必須要超越那些支配著某一特定學科的現有的研究規范。