Which of earth's resources can be transformed into a solid, a liquid, or a gas?
a. air
b. water
c. soil
d. wind

Let's take water: it definitely has three forms: ice, liquid and water vapor: it's definitely the correct answer!
 
Wind is just movement of air, so it can't be in any other state.

And as far as air and soil are concerned: some parts of them can also appear in three states, but not the air or soil generally, for example water is included in both of them and it can appear in the three states!

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.