PassageOne
Questions 46 to 50 are based on thefollowing passage.
At the base of a mountain in tanzania's Gregory Rift, Lake Natron burnsbright red, surrounded the remains of animals that were unfortunate enough tofall into the salty water. Bats, swallows and more are chemically preserved inthe pose in which they perished, sealed in the deposits of sodium carbonate inthe water. The lake's landscape is bizarre and deadly and made even more so bythe fact that it's the place where nearly75 percent of the world' s flamingos(火烈鸟) are born.
The water is so corrosive that it can burn the skin and eyes ofunadapted animals. FIamingos, however,are the only species that actually makes life in the midst of all that death.Once every three or four years, when conditions are right, the lake is coveredwith the pink birds as they stop flight to breed. Three-quarters of the world'sflamingos fly over from crystal islands that appear when the water is at aspecific level-too high and the birds can't build their nests, too low andpredators can move briskly across the lake bed and attack. When the water hitsthe right level, the baby birds are kept safe from predators by a corrosiveditch.
"Flamingos have evolved very leathery skin on their legs so theycan tolerate the salt water, "says David Harper, a professor at theUniversity of Leicester. Humans cannot, and would die if their legs wereexposed for any length of time. "So far this year, water levels have beentoo high for the flamingos to nest.
Some fish, too, have had limited success vacationing at the lake as lesssalty lagoons (25 9) form on outer edges from hot springs flowing into LakeNatron. Three species of tilapia(3#F 6) thrive there part-time."Fish havea refuge in the streams and can expand into the lagoons when the lake is lowand the lagoons are separate, Harper said. "All the lagoons join when thelake is high and fish must retreat to their stream refuges or die."Otherwise, no fish are able to survive in the naturally toxic lake.
This unique ecosystem may soon be under pressure. The Tanzaniangovernment has once again started mining the lake for soda ash, used for makingchemicals, glass and detergents. Although the planned operation will be locatedmore than 40 miles away, drawing the soda ash in through pipelinesconservationists worry it could still upset the natural water cycle andbreeding grounds. For now, though life prevails -even in a lake that killsalmost everything it touches.
What can we learn about Lake Natron?
根据关键词Lake Natron可以定位至第一段。该段第一句话指出湖水呈现亮红色，周围有许多不幸落入盐水中的动物的遗体。本段最后一句又接着指出，火烈鸟在这些生物当中却幸存了下来，可见A项论述符合原文意思。由此亦可排除C项和D项，许多鸟类以及捕食者并不适宜生存在这个湖之上。B项属于消极负面论述且有悖于常识，如果仍然知之甚少，本文的许多论述又从何而来，理应排除。
Flamingos nest only when the lake wateris at a specific level so that their babies can_______.
根据题干关键词可以定位至原文的第二段最后一句话，该句指出，当湖水处于合适的水位时，幼年时期的火烈鸟才能通过一条腐蚀性水沟免受捕食者侵害。故C为正确答案。
Flamingos in the Rift valley are uniquein that_______.
根据题干关键词可以定位至第三段第一句话。第二段第二句话表明火烈鸟是该湖唯一的物种。且定位句指出，火烈鸟腿上进化出了厚实的皮肤可以忍耐咸水，这是他们得以在该湖生存下来的原因。故B项正确。A项无中生有，故排除。第二段最后一句话指出，当湖水处于合适的水位时，幼年时期的火烈鸟才能通过一条腐蚀性水沟免受捕食者侵害。并非是火烈鸟在水沟内繁殖，故C项排除。D项无法证明火烈鸟与其他生物的独特之处，故亦排除。
Why can certain species of tilapiasometimes survive around Lake Natron?
根据题干关键词可以定位至本文倒数第二段。该段第三句话指出，鱼可以在溪流中避难，可以在水位低的时候进入泻湖，并且泻湖是分离的。A项中的take refuge对应原文中的have a refuge, less salty 是原文倒数第二段第一句中复现词，故A项正确。稳重为提及该鱼与捕食者的关系，亦未提及该鱼是否能够忍受温泉的温度，排除B和D。C项，与原文中的第二句话不符，原文表明只有当水位较低时，泻湖是分离的，鱼可以在泻湖之间自由游动。并非是自由游动，故排除C。
What may be the consequence ofTanzanian government's planned operation?
文章最后一段第一句话指出，这一独特的生态系统可能很快就会处于压力之下。该段第三句话后半句指出，有环保人士担心，政府的计划可能会扰乱自然水循环和繁殖地。因此，D项正确。A项“灭绝”一词用词过度，且无中生有，故排除。B项关于火烈鸟的迁徙路线亦未提及，故排除。C项overmining前缀“over-”属于过度用词，与原文最后一段第二句话不符，故排除。