Antarctica's icy lakes are home to a surprisingly diverse (various) community of viruses, including some that were not identified ( 确认) before.
At first sight, Antarctica's freshwater lakes don't seem very hospitable to life. They remain frozen for a good nine months out of the year, and they contain very few nutrients. Some of these lakes have little animal life and are ruled by microorganisms(微生物), including algae(海藻）, bacteria, protozoans (原生动物）and viruses.
With few animal and microbial predators (微生物的捕食性动物) around, viruses likely play an important role in controlling the number of other microorganisms, the researcher says. However, these viruses have been historically hard to study since many cannot be grown in a lab. But thanks to new technology, scientists can identify viruses without needing to grow them.
“We are just starting to uncover the world of viruses, and this is changing the way we think about viruses and the role they play in microbial ecosystems (微生物的生态系统)," said Antonio Alcami, a researcher from the Spanish Research Council.
A virus is little more than a package of DNA surrounded by a capsule structure. To survive, viruses must attack, or infect, living cells and use the host's equipment to reproduce.
Alcami and his colleagues analyzed DNA from viruses found in water samples collected from Antarctica's Lake Limnopolar, a surface lake on Livingston Island. They found nearly 10,000 species, including some small DNA viruses that had never before been identified. In total, the viruses were from 12 different families, some of which may be completely new to science, the researchers suggest.
The results show this Antarctic lake supports a virus community that's more diverse than most aquatic(水生的) environments studied in the world so far — a surprising find considering that the polar region is generally thought to have low biological variety due to the extreme environmental conditions. The scientists guess the newly discovered viruses may have got used to growing in such hard conditions.
The team also found the community of viruses changed greatly depending on the season. When the lake was ice-covered in the spring, small viruses ruled the liquid water under the ice mostly, but in the summer months when the ice melted, the lake was home to mostly larger viruses.
“It looks like a completely different lake in summer," Alcami said. The scientists think the change might be due to an increase in algae in the summertime, which affects the larger viruses.
The researchers hope to find out whether any of the viruses are unique to Antarctica. If so, that would shed light on (为…提供线索) whether microbial life developed independently in Antarctica, which has been separated for millions of years, or they were introduced there more recently.
The underlined word hospitable in Paragraph 2 is the closest in meaning to ________.

A．pleasant	B．disturbing
C．harmful	D．complex

Why are viruses likely to play an important role in the icy water environment?

A．Viruses are stronger and more ready to attack than other microorganisms.

B．Viruses are better at attacking other living cells than other microorganisms.

C．Viruses survive well in a place with few animal and microbial predators.

D．Viruses exist in larger quantities than other microorganisms.

What do scientists think of viruses on Antarctica?

A．Their discoveries of viruses there have made them change the way they think about viruses.

B．They were not surprised at all to find such a large quantity of viruses in an icy lake.

C．They think the viruses they found on Antarctica may do harm to people on earth.

D．They believe the discoveries of new viruses may help them find cure of diseases.

Which of the following about the viruses is NOT correct?

A．10,000 species of viruses including some newly-identified ones were found in the lake.

B．The community of viruses changed greatly depending on the season.

C．Scientists have found that many new viruses discovered there are unique to Antarctica.

D．The appearance of larger viruses in summer might have something to do with an increase in algae.

What is the passage mainly about?

A．A research center was set up on Antarctica by scientists.

B．Thousands of more deadly viruses have been found on Antarctica.

C．A huge diverse community of viruses have been found in a lake on Antarctica.

D．Viruses on Antarctica have made scientists realize that viruses are important.

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