一、语法填空(根据课文内容、依据语法规则完成下面短文）
John Snow was a well-known physician in London in the 19th century and wanted to help ordinary people 1________ (expose) to cholera which was the deadly disease of its day. It was 2________ (believe) that cholera was commonly caused by the bacteria in the air or people absorbed this disease into their bodies with their meals.
