地理学的研究是对地球作为人类居住地的研究。

The writer’s mission is to be a witness to his time, to speak for those who cannot speak.

The key is to set realistic customer expectations, and then not to just meet them, but to exceed them — preferably in unexpected and helpful ways.

数学的真正力量不在于它的复杂性，而在于它的简洁和优雅。