Last March, the H7N9 virus   hit Shanghai, Anhui, Jiangsu, Zhejiang and so on. It seemed that most people who were infected  with H7N9 had the common flu . Some people suffered from a fever or a cough.    Don't be afraid--it's not easy to be infected with the virus. Here is some advice to help you protect yourself when it comes.  Wash your hands. You need to wash your hands with soap and hot water before you eat, after you use the toilet, and after you touch animals, because your hands may carry viruses.  Cover your nose and mouth. When someone sneezes  or coughs, flu viruses can travel as far as one meter through the air, so you'd better stand a proper distance  while talking to someone who has a cold. And always cover your mouth and nose with a piece of paper when you sneeze or cough, and then clean your hands. Wear a mask . Some doctors say that masks can stop the flu as much as 80%, but if  you don't wash your hands often, it's no use wearing a mask. And it's necessary to wear the mask in the groups of people. Do sports often. Exercises will help make your body strong enough to resist the virus. What's the main idea of this passage?
It tells us how to wash hands. It tells us why we should use masks. It gives us some advice on how to protect ourselves when the H7N9 virus comes. It tells us what the H7N9 virus is.