The first plane ever to fly faster than the speed of sound was the X-1 in nineteen forty-seven.

VOA: special.2010.07.07

c We know it's very specific for light because in this equation is c, the speed of light. So any time you go to use this equation, if you're trying to use it for an electron, just ask yourself first, does an electron travel at the speed of light?

我们知道它只对光适用是因为在这个方程里有,光速，所以下次你们用这个方程前，如果你们要把它用到一个电子上，先问问你自己，电子的运动速度是光速吗？

麻省理工公开课 - 化学原理课程节选

In June,the Speed Sisters became the first all-female racing team to compete in the Speed Test, a popular race in the West Bank.

VOA: special.2010.07.30