阅读下面材料，在空白处填入适当的内容（1个单词）或括号内单词的正确形式。将答案填写在答题卡的相应位置。
As a well-known doctor in London, John Snow was willing to help ordinary people   (expose) to cholera. He knew that only when      cause of it was found could the     (dead) disease be controlled. He has two theories in mind explaining how cholera killed people.    was that cholera multiplied in the air without reason; the other was      people absorbed it into their bodies       their meals. After many   (investigate), he found the drinking water was to blame because the river      (pollute). Immediately John Snow told the people to remove the handle from the water pump       that it could not be used. Soon the disease began to slow down. To prevent the disease from     (happen) again, the water companies were instructed not to expose people to polluted water any more. Finally "King Cholera" was defeated