3．Pollution means adding dirty or harmful（有害的） things to land，air，water and so on．
As a result，they are no longer pleasant or safe to use．Pollution is bad for animals and plants，and it even makes people's health in danger．In our daily life，we can see different kinds of pollution in many places．There are three main forms of pollution：land pollution，air pollution and water pollution．
Land pollution is caused by solid waste，such as cans，bottles and some plastic things which aren't broken down quickly．It makes the environment look very bad．However，air pollution is more serious than land pollution．It is much worse in cities and towns because of the fumes（废气） from traffic and the waste from human（人类的） activities．When people drive their cars，fumes which are most made up of CO2，NO2 and SO2 are given off．After the gases get into the air，they may mix wit h clouds．Then they will become some harmful chemicals falling on the ground with rain．It is one of the reasons for soil erosion（土壤侵蚀） which is one example of water pollution．
Various kinds of pollution will cause many health problems．People have realized they must change this serious situation．There are many ways to control pollution．To develop alternative energy（替代能源）is very popular in many countries．China，for example，has made up its mind to be a leader in this field．It is trying hard to make full use of energy from the sun and wind．It has paid plenty of money to make electric cars and trains instead of traditional traffic．We should also take action to make our environment cleaner every day．Take cloth bags while going shopping and drive cars less．We have only one earth．We must take small steps no w to help protect our environment for the future wherever we are．
根据短文内容选择最佳答案．
46．The underlined word"solid"in the passage means"C"in Chinese．
A．气体 B．液体 C．固体
47．When people live in a polluted area，B．
A．they will control the use of alternative energy
B．their health will be in danger
C．they will get stronger and stronger
48．PictureAtells us how harmful chemicals pollute our environment．
49．Which of the following is TRUE according to the passage？C
A．There are only three forms of pollution．
B．China doesn't want to develop other kinds of energy．
C．Water pollution includes soil erosion．
50．The main idea of this passage should beA．
A．to introduce the kinds of pollution and the ways to control it
B．to introduce the harmful chemicals and soil erosion
C．to introduce the alternative energy and the ways to use it．
