不用圆规和曲尺，就不能画出方形和圆形。比喻做事要遵循一定的法则。

He who refuses to do arithmetic is doomed to talk nonsense.

实现明天的唯一限制是我们今天的疑虑。

井水越是甘甜，就越容易枯竭；树木越是高大，就越容易被砍伐。

If we want to feed the world, we must invest in smarter ways to raise livestock.