Mexico city is an example of how humans alter their environment because it was
a. one of the world’s largest cities
b. built on drained and filled lake beds
c. built after conquest by the spanish
d. once the capital of the aztec empire

Options a) b) and d) are true, and c can also be argued to be true, so the question is: which one of them is an example of altering the environment?

it's b- they drained the lake so that they can build settlements -so they altered the environment.

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.