from galaxy to galaxy from Saturn to Mercury from the Sun to Proxima Centauri from the Big Dipper to the Little Dipper
I gave my students this multiple choice question: One astronomical unit is the average distance between the Earth and the Sun. This unit is most often used to describe the distance between which two objects?

Only one answer is correct among these 4 choices:
- from galaxy to galaxy
- from Saturn to Mercury
- from the Sun to Proxima Centauri
- from the Big Dipper to the Little Dipper

Could you tell me which one is correct?

from Saturn to Mercury