S0 galaxies have spiral arms, but little to no gas and dust. This ...

[notis]

S0 galaxies have spiral arms, but little to no gas and dust. This is believed to happen because ____.
 
  a. their gas has been cannibalized by other galaxies
 b. they have had bursts of star formation during major collision the gas and dust formed new stars
  c. starburst events have used up all of the gas and dust in the disk
 d. gas and dust have been stripped from the galaxies as they pass through hot, intergalactic gas
  e. tidal interactions have forced the gas into the central bulge

Question 2

Astronomers no longer build large observatories in populated areas in order to avoid _______________.
 
  Fill in the blank(s) with correct word

[lou]

Answer to Question 1

d

Answer to Question 2

light pollution
radio interference

[notis]

Gracias!

[covalentbond]

Thanks for the timely response, appreciate it