请教while的用法

kun861010

Meteor showers and individual streaks of light that flash across the sky every night are generated when tingy flecks of celestial detritus, often no larger than grains of sand or of pebbles, burn up speeding through the atmosphere.
b.grains of sand or peples, burn up while speeding
就用这道题目来看，为什么原文没有while，这里一定要加while呢？

果汁软糖

http://forum.chasedream.com/GMAT_SC/thread-426759-1-1.html
这个贴很好哦 希望可以帮到你