the color of the galaxy the shape of the galaxy how many stars make up the galaxy how many planets make up the galaxy
I gave my students this multiple choice question: Classification of galaxies is based on which characteristic?

Only one answer is correct among these 4 choices:
- the color of the galaxy
- the shape of the galaxy
- how many stars make up the galaxy
- how many planets make up the galaxy

Could you tell me which one is correct?

the shape of the galaxy