Problem: Tree city and Leaf city were the two biggest cities in Boulderland. Tree city burned lots of gas and other fossil fuels, while Leaf city was very protective towards its environment. Which city exposed fewer people to asthma?

A: Leaf

Problem: The marine biologists studied two areas of the Black Sea. Area A, situated at the mouth of the Danube River, which presented high levels of water stratification, because of the fresh water discharged by the river; and area B, situated 35 miles south, where the water was less stratified and more oxygenated. Which of the two areas had less dense water?

A: Area A

Problem: Two lands applied different economical measures over the last decade. Greenland increased productivity so they became wealthy and prosperous. Iceland chose to increase taxation and expand its government, they had little money to invest. Which country had a lower satisfaction rate?

A: Iceland

Problem: Two sister cities had different environments. Shanghai had big problems with air pollution while Berna took very good care of the surrounding environment and air quality. Which city had people at increased risk of dying from other diseases?

A:
Shanghai