题目

①Mary is reading something about how to keep healthy on the Internet.Good sleep is important for your health. You need about eight hours’ sleep a night. Don’t eat or read in bed. A cup of milk before sleeping may help you get a good sleep. Go to bed at the same time before midnight(午夜) and get up at the same time every morning. For more information, please visit www.sleep.com.How often do you exercise? If you want to stay healthy, try to ②每天锻炼__分钟，每周三四次。For more information, please call Health Line at 180-2000.Studies show that the cold or flu virus(流感下列符号只有微观意义的是（ ）A．Cl2B．2N2C．CuD．CO2