想问个很简单的并列问题

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, burnup 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