A
(2020·宜春5月模拟)Strange ice rings in Siberia's Lake Baikal have puzzled scientists for decades，but now the mystery apparently has been solved.The answer: the rings are caused by warm，circular currents of water under the ice，called eddies(漩涡)．
The eddies' strong currents melt the ice at the edge，but weaker ones keep the center frozen.“Results of our field surveys show that there are warm eddies that circulate in a clockwise(顺时针的)direction under the ice cover，” said Alexei Kouraev，a hydrologist at the University of Toulouse，in a NASA statement.“In the eddy center，the ice does not melt—even though the water is warm—because the currents are weak，” he said.“But on the eddy boundary，the currents are stronger，and warmer water leads to rapid melting.”
During field work，Kouraev and his colleagues drilled holes near ice rings and set sensors capable of measuring the temperature and salinity(盐浓度)of the water to a depth of 700 feet.They found that the water in the eddies was 2 to 4 warmer than the surrounding water.
Most of the rings appear in March or April and have a width of about 3 to 4 miles—too big to recognize from the ground but easily seen from satellites above.Some rings were ephemeral while others lasted for weeks or even months.
Lake Baikal is the world's largest and deepest freshwater lake，according to Gizmodo.It's home to many varieties of fish not seen anywhere else in the world，and even a population of freshwater seals.
Researchers are still investigating what causes Baikal's eddies but think it's likely because of wind patterns，rivers that flow into the lake and the shape of the lake's coastline and bottom.
[语篇解读] 本文是一篇说明文。西伯利亚贝加尔湖多年的冰环之谜终于被解开了，答案就在于冰面下方的暖流漩涡；科学家们对漩涡的成因也有了初步判断，正在进一步的探索中。
1．Which word can best replace the underlined word “ephemeral” in Paragraph 4?
A．Steady. B．Current.
C．Fundamental. D．Temporary.
解析：词义猜测题。第四段该句中，while表示对比，ephemeral与lasted for weeks or even months“持久的”意义相反，是“暂时的”；B项意为“现在的、目前的”，与“过去的(past)”和“将来的(future)”意义相对，所以不对。A、C则与while后文意义不能形成对比。
答案：D
2．Why is the ice in the center of ice rings frozen while that at the edge is melted?
A．Because the center of ice rings is 2 to 4 warmer than the edge.
B．Because the currents in the center are less powerful.
C．Because it is too wide to be recognized or incited.
D．Because water in the center circulates in a clockwise direction.
解析：细节理解题。考查因果关系。从第二段第三句“In the eddy center，the ice does not melt—even though the water is warm—because the currents are weak”可知B项正确，因为暖流不够急促，所以造成只有冰的边缘才能溶解的现象；A项偷换概念，从第三段最后一句可知漩涡水温高于周边水温，不是冰环中心与边缘温差的比较，更不是题干原因；C项同样表述有误，从第四段第一句可知其讲述的是most of the rings，不是the ice in the center of ice rings，而且答非所问；D项表述不准确，从第二段第二句可知，water in the center应改为warm eddies，并且不是冰环中心保持冻结的原因。
答案：B
3．Which of the following statements about Lake Baikal's eddies is TRUE?
A．They are caused by hot and circular currents under the ice.
B．The ice in the center of Lake Baikal's eddies melts faster than that of the edge.
C．Researchers are uncertain about the exact reason of the eddies' existence.
D．Lake Baikal's eddies can only be measured at the depth of 700 feet.
解析：细节理解题。从文章最后一段可知C项正确。从最后一段第一句“Researchers are still investigating what causes Baikal's eddies...”可知Baikal's eddies的成因尚不明确，故A项错误，根据第一段第二句，A项可改为“the rings are caused by warm，circular currents...”；根据第二段第一句可知B项表述错误；根据第三段“Kouraev and his colleagues...set sensors capable of measuring the temperature and salinity of the water to a depth of 700 feet”可知D项偷换概念。
答案：C
4．What maybe the best title for the passage?
A．What's Causing the Giant Ice Rings in Siberia?
B．The Mystery of the Eddies in the Lake Baikal was Uncovered.
C．The Largest and Deepest Freshwater Lake—Lake Baikal.
D．Why Does the Edge of an Ice Ring Melt Faster?
解析：标题归纳题。此文主要介绍了西伯利亚贝加尔湖多年的冰环之谜的答案在于冰面下方的暖流漩涡，所以选A。解答漩涡之谜，并非本文重点，只在最后提及而已，B项表述有误；C项的范围太大；D项范围缩小，不足以概括文章。
答案：A
