Considering these facts, what do these places have in common? a) they are all major metropolitan areas. b) they are all areas without mass transit. c) they are all located in the northeastern united states. d) they are all located on the west coast of the united 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.