Earth and the Sun. the Moon and the Sun. Earth and the Moon. the Sun and the nearest star.
I am hesitating between 4 options to answer the following question, which option should I choose?
Question: An astronomical unit (AU) refers to the distance between
Possibilities:
- Earth and the Sun.
- the Moon and the Sun.
- Earth and the Moon.
- the Sun and the nearest star.

Earth and the Sun.