孔子说：“生来就知道的，是上等人；学习后才知道的，是二等人；遇到困难才学习的，是三等人；遇到困难也不学习的，这就是下等人了。”

I always tell my students that it's okay to make mistakes, as long as you learn from them.

Natural gas will play a critical role in the energy mix as we move toward a lower-carbon future.