Pollutants are introduced into surface or ground water
without a specific location source.

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.

The figure is not necessarily a parallelogram because only one diagonal is bisected and only one pair of sides is congruent.

Answer any resource, such as wood or solar energy, that can or will be replenished naturally in the course of time;