Natural experiments can provide valuable insights into economic questions.

瀑布歌唱道：“当我找到了自己的自由时，我找到了我的歌。”

Efficiency is the first virtue of engineers.

纠正错误的方法是用真理之光照射它们。

The world owes all its onward impulses to men ill at ease. The happy man inevitably confines himself within ancient limits.

The function of mental processes is to mediate between the needs of the organism and the demands of the environment.