The city's urban transportation system recently launched the first of up to five hydrogen buses.

VOA: special.2009.09.07

And so, each hydrogen has access to each electron, and now we have a satisfied system.

每个氢原子都有两个电子，这是一个令人满意的体系。

麻省理工公开课 - 固态化学导论课程节选

NASA officials cleared the flight after technicians fixed a hydrogen leak in the shuttle's fueling system, which delayed the launch from last week.

VOA: standard.2009.03.15