Spiral galaxies often appear bluish due to an abundance of
a. old stars.
c. young stars.
b. black holes.
d. white dwarfs.

C. young stars is what i would choose 

The answer is c. ok you little turkey

Air pollution: “combustion results in gases such as nitrogen oxides, nitrogen dioxide and particulates. the main causes of air pollution include transport, domestic combustion and industrial processes. pollutants from these sources can cause problems in the immediate vicinity and a distance away.”