(39-41)
       The earth is getting warmer with more and more greenhouse gases in the atmosphere.To better understand how greenhouse gases heat up our earth, we should first know   39  .A greenhouse is a special house made of glass for plants. It holds the heat of the sun so thatthe plants inside can grow better. Some gases in the atmosphere work like a greenhouse andcan keep the heat of the sun, so we call them greenhouse gases. Greenhouse gases help ourearth stay warm enough for animals and plants. In fact,   40  .
       There is, however, a big problem. More greenhouse gases than our earth needs areentering the atmosphere because of the way we live.   41  , with a great number of cars,there is too much CO2, a common greenhouse gas, and farm animals give off a lot of CH4,another greenhouse gas. If we want to “cool down” our earth, a good start is to change ourway of life, like driving less and eating less meat.

  gas 氣體 atmosphere 大氣層
【題組】39.
(A) how many greenhouse gases there are
(B) how long greenhouses have been used
(C) what a greenhouse is and how it works
(D) what greenhouse gases are and where they come from