(二)
         Most people agree that trees look nice. But trees can also help cities save money. A few years ago, the U.S. Forest Service studied trees in Chicago, Illinois. They learned that just one tree can save a city $402 over the tree’s lifetime.
         One way trees save money is by helping us save energy. Trees shade buildings from the summer sun. They also block the winter wind. That cuts down on the energy needed to heat and cool homes and offices. Saving energy means lower bills.
         Here is another way trees can help a city save money. When it rains, a city’s sewers fill up with water. To clean that water, cities spend lots of money. But trees’ leaves and roots soak up rainwater before it gets to the dirty sewers. With the help of trees, there is less water to clean.
【題組】43. What is the main idea of the story?
(A) Trees are pretty.
(B) Trees block winter wind.
(C) Air pollution costs money.
(D) Trees help save money.