Eighty billion dollars of that total was to be pumped into the U.S.economy to promote development of renewable energy, urban mass transit, high-speed rail systems and clean energy jobs.

VOA: standard.2010.02.25

Mass and energy -- I'm an open system, right?

质量和能量--我是个开系，对吧？

麻省理工公开课 - 热力学与动力学课程节选