A、By touching surfaces that have harmful organisms on them; B、By shaking hands with another person. C、By touching your mouth, no

Health experts say washing your hands reduces the spread of viruses and other organisms that cause disease. This advice may sound simple. However, experts say a lot of people do not follow it.
   A recent study found that many Americans fail to wash their hands after using public toilets. About thirty percent of the people left public restrooms without stopping to wash their hands.
   In the study, researchers asked 1,000 adults how often they washed their hands. The researchers observed almost 8,000 people at public toilets in five major American cities. Remits of the study were compared to a similar study clone in 1996.
   More than ninety-five percent of Americans questioned said they always wash their hands after using public restrooms. However, the study found that only seventy percent of them actually do so.
   The study also found that American men arc less likely than women to wash their hands after using a public restroom.
   The American Society for Microbiology announced the findings. Judy Daly works for the group. She admits that hand washing may seem an unusual subject to study. But she says hand washing is a very serious issue. Experts say hand washing is the simplest and most effective way to reduce the spread of infectious diseases.
   Infections can spread by touching surfaces that have harmful organisms on them. Shaking hands with another person also can spread infection. Harmful bacteria may enter your body if you touch your mouth, nose or eyes.
   Among the most common infections spread by hand are colds, influenza, and throat and ear infections. In addition, millions of food poisoning cases each year are blamed on people who prepare food but do not wash their hands. More serious diseases like cholera and hepatitis are spread this way, too.
   Many patients in hospitals also get infections. Some die from them. The spread of infections often is blamed on health workers who do not wash their hand after treating patients.
   The American Society of Microbiology has launched a public information campaign to get more people to wash their hands. Experts say following the correct method is important. You should wash your hand with soap and hot running water for at least fifteen seconds.
Questions:
15.Among the Americans questioned, how many of them don’t actually wash their hands after using public restrooms?
16.In the study, how many people were observed at public toilets in five major cities?
17.How do harmful bacteria enter your body?
18.How should you wash your hands?