How are you feeling today? Do you have a sorethroat? Are you coughing? Sneezing？These are all very common1 that tell your body is fighting a disease. Yourimmune system(免疫系统) works to protect you from diseases,but when it is weakened, you feel sick. The illness that you feel could be2 by one of two things： bacteria(细菌) or viruses(病毒).
Bacteria are things with just one cell( 细胞). They can be3 outside the body, but we also have trillions ofbacteria living in our bodies,4 thereare more bacteria than human cells in our bodies.5 don't worry: ninety-nine percent of these bacteriaare good for us. They6 usto feel happy, protect us from disease, and help us digest(消化)food. Your7 aloneincludes more bacteria than there are people on earth!8 , there are also bad bacteria that cause illnesses.We can treat these illnesses
with antibiotics(抗生素).
Viruses are9 than bacteria. They are little in size. They cannotexist without a host—a(n)10 or plant to live in. That person next to you who'ssneezing is the host of a virus. So, watch out! With each sneeze, he or she11 you over 100,000 virus cells, traveling at a speedof over 160 km/h! Once those cells get into your body, you become the12 . The virus then changes in order to make moreviruses in your body. If you get a virus, you can't13 it with antibiotics. You simply need to wait14 your body gets rid of it. Of course, you can protect15 from viruses such as the flu bywashing your hands. Over eighty percent of viruses are spread by touching an infectedperson or thing, so be sure to take care of yourself and stay healthy.
