Interstellar Extinction and the Reddening of Light by the Interstellar

Multiple Choice

Interstellar extinction and the reddening of light by the interstellar medium (ISM) are both caused by _____.

A) atoms and molecules in the ISM
B) only  atoms in the ISM
C) only molecules in the ISM
D) only dust in the ISM
E) dust, atoms and molecules of the ISM