题目内容：

第二节：语法结构（共10小题；每小题1.5分，满分15分）      

阅读下面短文，根据上下文填入适当的词语，或使用括号中的词语的适当形式

填空，并将答案填在答题卷标号为31~40的相应位置上。

We must have water to live. _____31_____the water we use is clean and fresh, it will make us ill. The animals _____32_____ (live) in and around lakes and rivers must also have clean water. Our rivers and lakes supply most of our water. The clear, blue water found by the first American settlers has changed. Many of our water sources are now _____33_____. They are filled _____34_____ dirt and waste which cannot be cleaned out. In many places, waste is not safe for most uses.

Lake Erie was _____35_____ a beautiful lake. Now it has been called “a dying lake”. Waste from nearby homes and factories has been dumped into _____36_____. Fish can no longer live in much of its polluted water. George Washington once called the Potomac “_____37_____ finest river in the world”. Now its water is no longer blue. Instead, it is soupy green. Suds, from detergents used to wash clothes, often cover the water of our rivers.

Water cannot _____38_____(make) in a factory. Once water is polluted it is _____39_____ to make it clean and safe again. We must learn to take care of the water _____40_____ we now have.