dust, gas, ice small, medium, large spiral, elliptical, irregular red giant, white dwarf, supernova
I gave my students this multiple choice question: Which of these are scientific classifications for galaxies in the universe?

Only one answer is correct among these 4 choices:
- dust, gas, ice
- small, medium, large
- spiral, elliptical, irregular
- red giant, white dwarf, supernova

Could you tell me which one is correct?

spiral, elliptical, irregular