【单选题】Suppose you go into a fruiter's shop, wanting an apple—you take up one, and on biting it you find it is sour you look at it, and see that it is hard and green. You take up another one, and that, too, ...
【简答题】阅读理解。 People and air pollution are often in the same places. This means that cities with large populations have the biggest problem of dirty air. Air pollution is caused by many different things. A ma...