广义相对论在某种意义上就是引力场的理论。

伦理道德的基础是理解爱和争斗在个体和社会中的作用。

There can be no permanent progress in the battle against hunger until the agencies that fight for increased food production and those that fight for population control unite in a common effort.

学习数学的最好方法就是做数学。