制革厂的废水是其价值观最真实的衡量标准。

The most profound ideas in mathematics often come from asking the simplest questions.

Sometimes the hardest thing in life is to know which bridge to cross and which to burn.

译文：读过的旧书要反复地阅读，读透读深才能知道书中的道理。赏析：经典的好书必须要反复阅读，常读常新，读懂书中的内容就会受益匪浅。

The only thing that scares me more than space aliens is the idea that there aren't any space aliens. We can't be the best that creation has to offer. I pray we're not all there is. If so, we're in big trouble.