Courtesy costs nothing. Lower the toilet seat after use. Let the people in the elevator exit before you enter. Return shopping carts to their designated areas. When you borrow something， return it better shape (filled up， cleaned) than when you got it.

没有牺牲，就没有自由。

写作是回忆，但也是遗忘。

学习一门新编程语言的唯一方法是用它编写程序。