Since kids get their looks from the genes of their parents it can't be A.
A tribe usually consist of people with the same race (Ex. Native American) so those wont usually be really "diverse."
Which leaves us with A and C. Now it comes to size. The larger and more populated an area the greater chance it has at being more diverse.
Since a city is larger than a small town I would say the answer is...
A. In a city
- justyourultimategeek