GRE Text Completion: JiJing 1373-GRE填空机经1373题 - Y878ZNB1ADMDBDPKA

Although the Kuiper Belt – the icy region of the solar system where Pluto orbits – was once much more crowded, today it has such a low density of objects that collisions between them are ____________. A. inconsequential B. ongoing C. unthinkable D. improbable E. continuous F. unlikely