GRE Reading Comprehension: ETS-GRE阅读ETS - TI1J2ZZBZDT5858T7

It can be inferred from the passage that it is because space is so vast that A. little of the interstellar material in it seems substantial B. normal units of volume seem futile for measurements of density C. stars can be far enough from Earth to be obscured even by very sparsely distributed matter D. interstellar gases can, for all practical purposes, be regarded as transparent E. optical astronomy would be of little use even if no interstellar dust existed