Due to overfishing, the number of fish in the ocean could drastically decrease. This will cause

A) an increase in the stability of the oceans
B) an increase in the salt content of the oceans
C) a decrease in the stability of the oceans
D) a decrease in the oxygen available in the oceans

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.

This country likely has a high total fertility rate (tfr).