The question is, are we happy to suppose that our grandchildren may never be able to see an elephant except in a picture book?

反馈是鲁棒控制系统的关键。

孔子说：“早上理解真理，晚上死也值得。”

追求数学知识是一段永无止境的旅程。

A story is never finished; it only stops.

社会制度应该建立在个人自由和财产权的基础上，这是繁荣和稳定的关键。