There are two types of germs: viruses and bacteria(细菌). Viruses are germs that can only live inside animals or plants. Viruses cause illnesses such as flu and measles(麻疹). Bacteria are tiny creatures. Some bacteria are good. They can help your stomach break down food. Other bacteria aren't so good. They can make you sick. Bacteria can cause sore throats(喉痛) and ear infections.