Most viruses can be found and killed by our immune system as soon as they enter our bodies.However，some viruses，for example，the coronavirus，are sneaky.They are difficult to recognize and find.These viruses can cause deadly diseases，like COVID﹣19.Human﹣to﹣human transmission can easily occur，and pandemic will therefore break out.Vaccination is by now a simple，safe and effective way to protect us from the diseases.

▲Vaccines are something that "looks" exactly the same as the viruses，mainly made from the viruses that are weakened or killed.They will not make us really ill.They only stimulate and activate our immune system to work，telling it something harmful is coming in.The immune system will know what the "viruses" look like，and send B cells（lymphocytes）or antibodies to find and kill them.Meanwhile，B cells will remember them for the next kill.A vaccine may also give us passive immunity by providing B cells taken from an animal or a human to play the same role.

Scientists have developed more than 180 vaccines to fight against COVID49.The technical approaches of these vaccines can be a little different，but their aims are the same.

Take the inactivated vaccine as an example.In an inactivated vaccine，the coronaviruses are already killed or made into the ones unable to produce more new viruses.When the immune system "sees" them，it will try to kill them.The question is：without enough these viruses• how can B cells remember them？That's why we need to take the vaccine more than one time.Though this vaccine is safe，it might not be as effective as it is expected to be.

The live﹣attenuated vaccine is different.In this vaccine，the viruses are weakened，but they are alive.They can produce enough new viruses to train the immune system to kill and remember them，so people only need to take the vaccine once.The live﹣attenuated vaccine is considered the most effective，but there is a worry：what might happen once these viruses wake up？

Therefore，although vaccination is by now one of the best ways to protect us from COVID﹣19，it can be better.

（1）The coronavirus can 　 　.

A．	not be killed
B．	not be found
C．	cause deaths
D．	stop pandemic

（2）Which of the following can be the best topic sentence of Paragraph 2？ 　 　

A．	Vaccination can provide us with B cells.
B．	Vaccines are made from different viruses.
C．	Vaccination can prepare us against viruses.
D．	Vaccines won't make us ill as the viruses do.

（3）Compared to the inactivated vaccine，the live﹣attenuated vaccine 　 　.

A．	needs taking more than once
B．	is equally safe
C．	contains viruses that are killed
D．	is more effective

（4）What can we learn from the passage？ 　 　

A．	Vaccination is good enough to treat COVID﹣19.
B．	The immune system can be more effective with vaccines.
C．	The viruses in inactivated vaccines can make new viruses.
D．	180 vaccines have been developed to fight against diseases.