A new report by environmental ______________ The Nature Conservancy lays out how trees could pave the way to cleaner air and cooler cities. Using ______________ information on forest cover paired with air pollution data and population ______________ for 245 cities, researchers found that trees have the biggest health ______________ in densely populated, polluted cities like Delhi, Karachi and Dhaka. The Conservancy and the C 40 Cities Climate Leadership Group presented the findings of their global survey this week at the American Public Health Association meeting in Denver, Colorado.