Which Statement About Dark Dust Clouds Is True

Which statement about dark dust clouds is true?

A) They block the vast majority of radio waves from our Galaxy.
B) They can be penetrated only with shorter waves, such as UV and X- ray.
C) Hydrogen and helium are the chief absorbing and scattering agents.
D) They comprise the majority of the mass of the Galaxy.
E) They can be penetrated only with longer wavelengths such as radio and infrared.