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.

The correct answer is:   [b]:   "has no atmosphere" .