Acquiring this simple and non-polluting form of electric light,he points out, promotes education, public health,economic security and a cleaner environment.

VOA: standard.2009.12.13

Light travels basically a foot in a nanosecond. Simple rule of thumb.

光行进的速度是每纳秒一英尺,很简单的经验法则了。

麻省理工公开课 - 计算机科学及编程导论课程节选

Light travels basically a foot in a nanosecond. Simple rule of thumb.

光行进的速度是每纳秒一英尺,很简单的经验法则了。

麻省理工公开课 - 计算机科学及编程导论课程节选