The point from which all other lines of latitude measure distance is
a.
the absolute location
b.
the north pole
c.
the prime meridian
d.
the equator

D. The Equator Latitude are the horizontal lines measuring how far North/South a place is from another.

Europeans are more concentrated in urban areas.

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.