Coal keeps America competitive in the world.

The concept of nondeterminism in computation is one of the most important ideas in computer science.

I was taught that the way of progress was neither swift nor easy.

成功的关键不仅仅是努力工作，而是聪明地工作并适应变化。

Man is much more than he thinks.

形容世事变化无常，难以预测。