1 . Americans are now allowed to get a COVID-19 vaccine （疫苗）. But the process in America is not going as smoothly as some had hoped. Many people are still facing a wait for their first shot. Moreover, the vaccines aren't available to kids under 16 yet. That's because scientists have only tested if the vaccine works in adults.

The good news is that there are two companies, Moderna and Pfizer, making COVID-19 vaccines. They are now running clinical trials（临床实验）to test their vaccines in teens and kids. Volunteers are given a treatment plan and then evaluated after.

Clinical trials are designed with safety in mind and usually done in adults first. They work like this: volunteers get placed into one of two groups. One group receives the vaccine. The other group gets a placebo. This is a shot given in the same way as the vaccine but with no effect. Scientists can compare the effects of the real vaccine against the placebo to see if the vaccine works. Researchers want to know everything that a person experiences when they get the shot, so they can detect any harmful effects. If anything did happen, the trial would stop immediately.

Some teens are eager to volunteer because they want to help people. Maybe you're the right age to be part of a clinical trial for the COVID-19 vaccine. Why not volunteer For A Vaccine Trial? Interested kids should read about the trials because every trial has risks. They should talk to their doctor and weigh the benefits and risks. Every vaccine has rare side effects in a few patients.

If you want to participate in a trial, you can try to sign up online by just clicking here, clinicaltrials gov. which lists every clinical trial in the US, including COVID-19 vaccine trials.

1. Why kids under 16 can't get a COVID-19 vaccine?

A．Because the vaccine is too hard to get.

B．Because the vaccine is too expensive for them.

C．Because they are not at the risk of getting COVID-19.

D．Because the effectiveness of the vaccine for kids hasn't been tested .

2. What does the underlined word "placebo" in paragraph 3 refer to ?

A．A substance to comfort patients	B．A pill to treat patients
C．A prize to award patients	D．A way to cure patients

3. What's the purpose of this article?

A．To tell American adults they can get a COVID-19 vaccine.

B．To inform that American children can't get a COVID-19 vaccine.

C．To give information about clinical trials of vaccines in teens and kids.

D．To provide information for potential volunteers on trials.

4. Where does this passage probably come from?

A．Newspapers.

B．Magazines.

C．Internet.

D．Textbooks.