As paleontologists can tell, Neanderthals （尼安德特人）died out around 40，000 years ago. But they did not vanish from the Earth entirely. In the past decade it has become clear that Neanderthals mated with the ancestors of modern humans, and that some of those unions produced offspring （generations to follow）. The result is that almost half of the Neanderthal genome survives, spread in small quantities among most modern people's DNA. The exception is those with mostly African ancestors, for Neanderthals seem never to have lived in Africa.
Such genes have been associated with everything from hairiness to fatness. Many seem to be related to the immune system, and to affect the risk of developing diseases including lupus, Crohn's disease and diabetes.
A pair of recent papers suggest Covid-19 belongs on that list as well. Two long DNA strings, both inherited from Neanderthals, appear to have resistance or sensibility to severe Covid-19， depending on which is present.
The work was led by Hugo Zeberg and Svante Paabo at the Max Planck Institute for Evolutionary Anthropology in Leipzig, whose researchers pioneered the study of Neanderthal DNA.
Their first paper, published in Nature in September, described one Neanderthal DNA string, known as a "haplotype"（单体型），which is associated with a higher risk of serious illness.
Having one copy of the haplotype, which is found on the third of the 46 chromosomes possessed by humans, doubles the chances of a trip to intensive care. Those unlucky enough to possess two copies, one from each parent, face an even higher risk.
That genetic bad luck is not evenly distributed. It is most common among people of South Asia, with 63 percent of the population of Bangladesh carrying at least one copy； and among Europeans, where the rate is around 16 percent. As expected, it is almost absent from Africa. More strikingly, it is also very rare in Eastern Asia.
Exactly what the haplotype does is not clear. One gene within it affects a protein that interacts with the cellular receptors （细胞受体）that SARS-CoV-2 （the virus which causes Covid-19）uses to enter cells and control them.
The haplotype is also thought to be involved in the production of signalling proteins,called cytokines,which help to regulate the immune system. An overly aggressive immune response is one mechanism by which Covid-19 kills.



Who are the most likely to carry the haplotype according to the study？ ______

A. Eastern Asians.
B. Africans.
C. Europeans.
D. South Asians.

What can we learn about the study？ ______

A. The haplotype is equally distributed among people in different races.
B. Covid-19 kills partly because the immune system responds to SARS-CoV-2 abnormally.
C. The haplotype appears to have resistance or sensibility to severe Covid-19.
D. People unlucky to have two copies of the haplotype are sure to suffer from serious illness.

What is the main idea of the last two paragraphs？ ______

A. Why the Neanderthal genome is related to a higher risk of serious illness.
B. What effects the haplotype has on different people in different races.
C. Why the haplotype makes people have a higher risk of Covid-19.
D. What the haplotype does to affect and regulate the immune system.

What will the author probably write in the next paragraph？ ______

A. The second study on Covid-19.
B. The previous study about Neanderthals.
C. The other Neanderthal DNA string.
D. The sensibility to severe Covid-19.