经济发展理论研究的是经济系统如何产生不断改变它的力量。

The plastic industry must evolve or become obsolete. Sustainability is no longer an option—it's a necessity.

译文：每次见到贫寒的读书人，快要发达时，脸上一定有一片谦和之光散发出来。

We are healed of a suffering only by experiencing it to the full.

The future of coal lies not in its quantity but in how cleanly and efficiently we can use it.