[問題] Prep-T2-Q144

[lindababy]

Meteor showers and individual streaks of light that flash across the sky every night are generated when tiny flecks of celestial detritus, often no larger than grains of sand or of pebbles, burn up speeding through the atmosphere.
 
(A) grains of sand or of pebbles, burn up speeding
(B) grains of sand or pebbles, burn up while speeding
(C) grains of sand or pebbles, which burn up while speeding
(D) a grain of sand or pebble, which burns up as it speeds
(E) a grain of sand or a pebble, burns up when it speeds

答案(B)

只想請教一個問題
when/while等這樣的字眼，不是都一定要搭配完整的子句嗎?
但正確答案看來看去都只有一個主句

Meteor showers and individual streaks of light that flash across the sky every night are generated when tiny flecks of celestial detritus, often no larger than grains of sand or of pebbles, burn up while speeding through the atmosphere.

我了解while speeding省略了主語tiny flecks of celestial detritus
從Meteor開始到when......完整的句構
但那while呢?就沒有完整的句子可以搭配了
還是說....我搞錯了這裡while的用法?

請大家指教指教.....打結了~