题目内容：

    Why are some people better able to beat the flu than others? Part of the answer, according to a new study, is related to the first flu strain we met in childhood.

Scientists from UCLA and the University of Arizona have found that people’s ability to beat the flu virus is decided not only by the sub types of flu they have had throughout their lives, but also by the sequence (顺序) in which they have been infected by those viruses. Their study was published in PLoS Pathogens. The research offers an explanation for why some people become much worse than others when infected with the same strain of the flu virus.

In addition, UCLA scientists, including Professor James Lloyd-Smith, who was also a senior author of the PLoS Pathogens research, recently completed a study that analyzed (分析)travel-related screening(筛查) for the 2019-nCoV. The researchers reported that screening travelers is not very effective for the 2019 coronavirus ― that it will catch less than half of infected travelers, on average ― and that most infected travelers cannot be found out, meaning that they have no symptoms(症状)yet, and are unaware that they have been at high risk. So stopping the spread of the virus is not simply a matter of improving screening methods at airports and other travel centers.

“This puts the responsibility on government officials and public health officials to follow up with travelers after they arrive, to separate them and trace(追踪) their contacts if they get sick later,” said Lloyd-Smith, a UCLA professor of ecology and evolutionary biology(生态学和进化生物学). “Many governments have started to impose quarantines (隔离), or even travel bans, as they realize that screening is not enough to stop the spread of the coronavirus.”

One major concern, Lloyd-Smith said is that other countries, especially developing nations, lack the infrastructure(基础设施)and resources for those measures, and are therefore vulnerable to importing(输入) the disease. “Much of the public health world is very concerned about the virus being introduced into Africa or India, where large populations exist that are not able to receive advanced medical care,” he said.

1.Why is the scientists’ research very important?

A.It explains the cause of the flu virus. B.It reduces the risk of people being infected.

C.It analyzes(分析) people’s ability to fight off the virus. D.It stops the spread of the flu virus all around the world.

2.What do we know about the novel coronavirus from Paragraph 3?

A.Travelers are at high risk of being exposed to it.

B.It is more difficult to stop its spread than expected.

C.Most travelers infected with it are detected by screening.

D.It spreads especially quickly at airports and railway stations.

3.Why does the writer mention Lloyd-Smith’s words in Paragraph 4?

A.To persuade people not to travel. B.To provide a method to kill the virus.

C.To show the harmful effects of the virus. D.To stress(强调) the responsibilities of officials.

4.Which of the following best explains the underlined word “vulnerable” in the last paragraph?

A.Easy. B.Impossible. C.Responsible. D.Indifferent.