Discription of application of the energy source

Fossil fuels are source of electricity and heat for homes. Hydro-power is used to create large volume of electricity. Solar power use light reflection mirrors to trap the energy and convert into electricity. Bio energy is used as an alternative to traditional oil.  Geothermal power is derived from the heat beneath earth's surface.

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.

I'm pretty sure it's c. extremely gradual but not 100% sure though.