1 . We are surrounded by the news about COVID-19 and other viruses (病毒), but how much do you really know about them? Viruses that infect (传染) humans nearly always cause illness. Fortunately, just as we know a lot about how viruses harm us, so do we know how to prevent them. These facts are a good place to start.

·Being infected without signs is possible

Some viruses, including those that cause herpes, COVID-19, and AIDS, can be spread through asymptomatic (无症状的) people and presymptomatic (症状发生前的) people, according to the Centers for Disease Control and Prevention (CDC). Some of them may even be “super-spreaders”, infecting dozens to hundreds of other people without even realizing it. Take action to prevent spreading viruses even when you don’t feel sick.

·Hand washing is protective

Wash your hands. This is a piece of advice given by World Health Organization (WHO). Make sure to wash your hands with soap for at least 20 seconds and dry your hands on a clean towel. Don’t use air dryers in public restrooms.

·Regular exercise is helpful

Do regular exercise. Regular exercise, which can include taking quick walks, has been shown to improve your immune system, thus reducing your possibilities of developing a cold or the flu. But don’t overdo it, for example, training for a long marathon without professional guidance.

·Herd immunity (群体免疫) is hard to achieve

You may have read that you needn’t get vaccinated (疫苗) if you live in a place where most people have had the disease or the vaccine, allowing you to make use of herd immunity. But effective herd immunity requires that more than 90 percent of the population be vaccinated against a disease.

1. Which of the following is TRUE about “super-spreaders”according to the text?

A．They have many signs of the illness.

B．They may infect a lot of people.

C．They prevent spreading the viruses.

D．They realize they are spreading viruses.

2. The following ways are helpful to prevent viruses except          .

A．washing hands for enough time

B．doing exercise regularly

C．avoiding using air dryers in public restrooms

D．training for a long marathon without professional guidance

3. A man can have herd immunity against a disease when           .

A．lots of people in his place have the vaccine

B．over 9/10 of the people in his place are vaccinated

C．people in his place are fighting against the disease

D．most people in his place are infected by the disease

4. What is the text mainly about?

A．Some virus facts that we should know.

B．Some news about COVID-19 and other viruses.

C．Some facts about how to fight against COVID-19.

D．Some facts that cause COVID-19 and other viruses.