What conditions gave rise to the number of languages spoken in Oceania? Would it be accurate to state
that nearly half the languages spoken in the world are
in Oceania?

The many islands separated by water made for very little to no contact with one another. This lead to the formation of different languages and cultures.

This is all you, but i can give you some topics that you could try. if it rained when you want to do something outdoors, it 'limits' that human activity. maybe you want to do an experiment that goes throughout the whole year and you have to have above freezing the entire year. this 'limits' your activity. i thought of those just off of the top of my head. something that gets to me that might be getting to you is you are thinking too hard about what to do. think simply, and if it is too simple, then bump it up just a little bit.