27．The earth is becoming warmer and warmer.It is believed that people have caused global warming （1）
burning fossil fuels like coal，natural gas and oil to produce energy.Some by-products of this process （2）
（call） "greenhouse"gases.These"greenhouse"gases can keep （3）
earth warm enough for us to live on.However，when（4）
（quantity） of extra carbon dioxide are put into the atmosphere，the global temperature tends（5）
（go） up.Although scientists have different opinions about the future effects of global （6）
（warm），most believe that the temperature of the earth would increase by about 5 degrees over the next 100 years， （7）
may cause the sea level to rise，bring about floods，storms，droughts，the spread of diseases and the disappearance of species. （8）
a famous scientist named Hambley says more carbon dioxide will make plants grow （9）
（quick）；crops will produce more and that it will encourage a greater range of animals.
Greenhouse gases continue to build up the atmosphere.The climate （10）
（keep） on warming for decades or centuries even if we start reducing the amount of greenhouse gases.What will be the future results of global warming？We will wait and see.
