John Snow was ____ expert doctor in London in the 19^th century. At that time a lot of people were infected with cholera and died , so he was ____ (determine) to find the cause of it so that he could help those____ (expose) to it .He began to gather information when another outbreak hit London in 1854. He marked on the map the exact places ____ the dead people had lived and found that most of____ (die )were near a water pump .After careful investigations John Snow announced____ certainty that water ____ (carry ) germs was ____ (blame) for the spreading of cholera . In order to prevent this ____ (happen) again , he suggested that the source of all the water supplies ____ (examine) and instructed the water companies not to allow people to drink the polluted water any more . At last “King Choler” was defeated .