81.  We May never use it up.

82.  This problem May result from several reasons: First, the population is increasing, which leads to more need for water.

83.  And fresh water May also come from rain and snow.

84.  Thus, we May have a beautiful world with plenty of fresh water.

85.  Finally, May be the most important, is the pollution.

86.  It May lie in serval factors: the increase of popullation , the increase use of industries and pollution.

87.  It is very important for us to protect the water source in case it might be polluted.

88.  We May often think that there is abuntent of fresh water on the earth and there is no possible we run out of fresh water.

89.  A lot of people May think there is a lots of fresh water on the earth.

90.  What's more, they might give out chemical dusty with water.