Provide your best answer for the following question. Give ONLY the answer, no other words or explanation.
For example:

Answer: <most likely answer, as short as possible; not a complete sentence, just the answer!>.

The question is: During a presentation on astronomy, Professor Williams discussed various measurements in space. Which objects was she referring to when she talked about how astronomical units (AU) were determined?
the Sun and Earth
The AU is a unit of measurement for distances within the solar system, specifically the average distance from the Earth to the Sun.