Mexico City is sinking every year.
Why it is true
Built on the dry bed of Lake Texcoco, Mexico City is sinking between 10 and 15 centimeters per year as the ground compacts. Over the last 60 years, parts of the city have dropped nearly 10 meters.
Source: Geology
Would you rather be asked first?
This is the reading side of the site, so the answer is in the sentence above — that is the whole point of it. Test yourself works the other way round: the question comes on its own, and the fact and the explanation only appear once you have answered.