"Flamingos have evolved very leathery skin on their legs so they can tolerate the salt water," says David Harper, a professor at the University of Leicester. " Humans cannot, and would die if their legs were exposed for any length of time." So far this year, water levels have been too high for the flamingos to nest.
Some fish, too, have had limited success vacationing at the lake as less salty lagoons (泻湖) form on the outer edges from hot springs flowing into Lake Natron. Three species of tilapia (罗非鱼) thrive there part-time. "Fish have a refuge in the streams and can expand into the lagoons when the lake is low and the lagoons are separate," Harper said. "All the lagoons join when the lake 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 Tanzanian government has once again started mining the lake for soda ash, used for making chemicals, glass and detergents. Although the planned operation will be located more than 40 miles away, drawing the soda ash in through pipelines, conservationists worry it could still upset the natural water cycle and breeding grounds. For now, though, life prevails – even in a lake that kills almost everything it touches.
46. What can we learn about Lake Natron?
A) It is simply uninhabitable for most animals.
B) It remains little known to the outside world.
C) It is a breeding ground for a variety of birds.
D) It makes an ideal habitat for lots of predators.
A. 原文第一段 ， 在坦桑尼亚GF山脚 ， Lake Natron有着亮红色的光 ， 它被不幸落入盐湖的动物的尸体包围着 。蝙蝠 ， 燕子和更多其他动物 ， 被化学地以他们生还最后一个的姿势保存 ， 封印在水中的碳酸钠沉淀中 。这个湖的地貌是奇特并且致命的 ， 以及被一个事实——这个地方是世界上几乎75%的火烈鸟的出生地 ， 变得更加如此 。因此可以得出 ， 这个湖水对于大部分动物是致命的 ， 不适宜生存 ， 选A 。B选项 ， 外界不了解这个地点 ， 未提及 。C选项 ， 它是各种鸟的生殖区域未提及 。D选项对于很多捕食者是理想的居住地 ， 未提及 。
47. Flamingos nest only when the lake water is at a specific level so that their babies can ______.
A) find safe shelter more easily C) stay away from predators
B) grow thick feathers on their feet D) get accustomed to the salty water
C.原文第二段第四句开始 ， 清晰定位water is at a specific level ， 世界上3/4的火烈鸟从其他盐湖地区飞到Rift Valley并在盐结晶岛上筑巢 ， 这些盐结晶岛只有在特定水位时才会出现——水位太高时鸟无法筑巢 ， 水位太低捕食者能吃迅速越过湖床并且攻击他们 。当水位处于正确高度时 ， 婴儿火烈鸟是安全的由于一个腐蚀性的沟壑阻止了捕食者 。C选项为正解 。
48. Flamingos in the Rift Valley are unique in that _______.
A) they can move swiftly across lagoons C) they breed naturally in corrosive ditches
【classmate workmates】B) they can survive well in salty water D) they know where and when to nest
B. 此题并不能清晰定位 ， 根据顺序原则 ， 找到第三段第一句 ， 火烈鸟已经进化出了非常厚的的皮肤因此他们能够忍耐高盐的水 。直接选B ， ACD未提及 。
49. Why can certain species of tilapia sometimes survive around Lake Natron?
A) They can take refuge in the less salty waters.
B) They can flee quick enough from predators.
C) They can move freely from lagoon to lagoon.
D) They can stand the heat of the spring water.

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