"The world has been a very violent place in oil frontier places when we have had enough to go round.

VOA: standard.2009.10.20

I think that these countries are somewhat trying to manage this oil risk but they can't yet get onto the frontier.

我想这些国家或多或少,都试着控制石油风险,但他们根本无法达到有效边界。

耶鲁公开课 - 金融市场课程节选

Where are we on this frontier regarding oil in the United States?

考虑到美国拥有的石油的话我们又在哪呢？

耶鲁公开课 - 金融市场课程节选