You didn't provide the list of choices, but I can tell you some things that were seen as bases of the classical conventions of beauty.
Geometry was one such source -- seeing beauty in symmetry and consistency of shapes.
In a similar way, astronomy even provided a source, as those who looked out to the heavens saw what they referred to as the "music of the spheres," the way that planetary bodies all moved in harmony as a system.
The human form was a very strong model for determining classical beauty, and artists did much study and depiction of the human form.
This questions has many different answers. None of us can really help you since these are personal questions for yourself. I would help but for example, I don't know if you're interested in learning to play an instrument.
