As rain begins to fall from the clouds, it is very pure. However, as it falls through the air it dissolves some of the gases in the air ,It also collects bits of dust and microbes(微生物)that are floating in the air, When the rain reaches the ground it begins to pick up more dust and dirt, Many kinds of mineral substances dissolve in the water ,Sand and nud cannot dissolve in water. Since water is so important to us, it is very important that the water we use should be clean , Otherwise, we might get some of the diseases that are carried by water Many microbes are harmful ,They are so small that we cannot see them ,These microbes must be removed or killed before the water is not clean, people who drink this water may get these diseases, Thus , to provide people with clean water, the government purifies the water. Purification is a long process and consists of three stages: storing ,purifying and distributing ,The first stage is storing , Man-made lakes called reservoirs are used for this purpose ,Water from the rains ,other lakes, streams and rivers is collected in the reservoirs ,This water is usually dirty and muddy. In the second stage shich is purifying , water from the reservoirs is filtered in a special pond, Stones, sand and other unwanted tiny things are caught in it, After that, tiny microbes are still present in the water ,These microbes are removed by “airing ”the water and by adding a chemical substance called chloring(氯)to the water ,This kills all the microbes in the water ,A fter this the water can be safely used for drinking. The third stage is the distribution of the purified water to homes ,hospitals, offices ,factories and other places, This is done through a network of pipes of various sizes, These pipes must be make of a suitable material. 小题1:From Paragraph 1, we can learn that A．Rain has contained gases when it forms in the clouds B．Dust and microbes are dissolved in rain when rain falls on the ground C．The closer rain is to the ground, the more impure things it contains D．Sand and mud are things rain collects when it falls through the air 小题2:According to Paragraph 2 ,the following statements are wrong except that A．All the microbes in water are harmful so water must be purified B．some diseases can spread through drinking water if it is not clean C．Water is safe to drink if only harmful microbes are removed from it D．it is the govrnment’s responsibility to make drinking water clean 小题3:What can we know about man-made lakes? A．It is used through the whole process of purification B．Only rain water can be collected and stored in it C．Water collected can be stored and filtered in it D．Water from them contains a lot of impure substances 小题4:What is the function of the chemical substance chlorine? A．to air the water B．to catch tiny things C．to kill microbes D．to remove harmful gases 小题5:What is probably this passage? A．A news report B．A book review C．A magazine article D．A school paper