Toads are Arthritis and in Pain

　　Arthritis is an illness that can cause pain and swelling in your bones. Toads, a big problem in the north of Australia, are suffering from painful arthritis in their legs and backbone, a new study has shown.

　　The toads that jump the fastest are more likely to be larger and to have longer legs.46

　　The large yellow toads, native to South and Central America, were introduced into the north-eastern Australian state of Queensland in 1935 in an attempt to stop beetles and other insects from destroying sugarcane crops. Now up to 200 million of the poisonous toads exist in the country,and they are rapidly spreading through the state of Northern Territory at a rate of up to 60 km a year.

　　The toads can now be found across more than one million square kilometers. 47 A Venezuelan poison virus was tried in the 1990s but had to be abandoned after it was found to also kill native frog species.

　　The toads have severely affected ecosystems in Australia. Animals, and sometimes pets, that eat the toads die immediately from their poison, and the toads themselves eat anything they can fit inside their mouth. 48

　　A co-author of the new study, Rick Shine, a professor at the University of Sydney, says that little attention has been given to the problems that toads face. Rick and his colleagues studied nearly 500 toads from Queensland and the Northern Territory and found that those in the latter state were very different. They were active, sprinting down roads and breeding quickly.

　　According to the results of the study, the fastest toads travel nearly one kilometer a night.

　　49 But speed and strength come at a price- arthritis of the legs and backbone due to constant pressure placed on them.

　　In laboratory tests, the researchers found that after about 15 minutes of hopping, arthritic toads would travel less distance with each hop (跳跃). 50 These toads are so programmed to move,apparently, that even when in pain the toads travelled as fast and as far as the healthy ones,continuing their relentless march across the landscape.

　　A. But this advantage also has a big drawback--up to 10% of the biggest toads suffer from arthritis.

　　B. The task now facing the country is how to remove the toads.

　　C. But arthritis didn't slow down toads outside the laboratory.

　　D. Toads with longer legs move faster and travel longer distances while the others are being left behind.

　　E. Toads are not built to be road runners-- they are built to sit around ponds and wet areas.

　　F. Furthermore, they soon take over the natural habitats of Australia's native species.

　　46.A。从原文来看，第一段的首句要说关节疾病(Arthritis)的危害。空白处前面一句讲到那种腿长的大蟾蜍跳得快，空白处应该接着谈蟾蜍这种腿长的优势，所以A(但是这个优势也有一个大的缺陷，即近10%的蟾蜍会得关节疾病)比较合适，不仅接着谈长腿的优势，同时也点出了“关节病”这一主题词。

　　47.B。从原文来看，空白处前面一句讲的是蟾蜍现在已经蔓延到超过l00万平方公里的区域，说明蟾蜍开始泛滥，而空白处后一句说的是一种委内瑞拉病毒在90年代开始用来消灭蟾蜍，但之后发现它也杀本地的青蛙物种，所以就不得不放弃了，所以空格处应填入与消除蟾蜍有关的选项，故B(现在这个国家面临的任务就是如何消除蟾蜍)符合原文。

　　48.F。从原文来看，第三段的首句说蟾蜍严重影响了澳大利亚的生态环境。空白处前面一句讲到吃蟾蜍的动物和宠物都被毒死了，而且蟾蜍吃掉了能吃的一切。空白处填入与生态环境受到蟾蜍影响有关的语句，故F(并且，它们很快就占据了澳大利亚本地物种的自然栖息地)是正确答案。

　　49.D。从原文来看，空白处前面一句讲到研究结果表明，最快的蟾蜍一个晚上能跑近l公里。空白处后一句讲的是这种速度和力量却是要付出代价的。因此，空白处谈论的应该还是有关速度的话题，所以D(长腿的蟾蜍移动较快并能移动较长的距离，而其他蟾蜍则落在后面)比较符合原文语义。

　　50.C。从原文来看，空白处前面一句讲到研究者发现跳跃约l5分钟后，有关节炎的蟾蜍每一次跳跃的距离会递减。空白处后一句提到蟾蜍是程序化的移动，即使有关节病的蟾蜍，也跟健康的蟾蜍跳得一样快，一样高远。前后有转折关系，所以C选项(但是关节疾病不会降低蟾蜍的速度)是正确答案。