题目内容
20．Scientists in Colombia have trained a team of rats to help remove land mines from the countryside．Land mines are small bombs （炸弹） hidden in the ground and designed to explode when someone steps on them．When trained，the rats can smell special metals in the mines and then signal to their human team．Then why use rats for such an important job？
In the past，dogs have been used to find bombs．Rats have a good sense of smell and can respond to orders，just like dogs do．But rats are much lighter than dogs．They stand less of a chance of setting off the mines，which explode under a certain amount of weight．What's more，the best rats are cheaper to keep than dogs．It costs about the same amount of money to take care of one dog as it does 70rats．
The rats have already been used in Tanzania，an African country with many land mines．Luisa Fernanda Méndez and her team in Colombia are training the even lighter Wistar rats．These are the white rats with red eyes that scientists often use in laboratory experiments．"They even train their babies to perform their jobs，which saves us a lot of time，"Méndez said．
Colombia has the second-highest rate （比率） of deaths from land mine accidents in the world．Last year，land mines killed 695people-56of whom were children．A criminal （犯罪的） group called the Revolutionary Armed Forces of Colombia，or FARC，as well as other organizations，have placed the mines．FARC are strongly against Colombia's government．The group has placed mines all around its own bases and in many places in the countryside．
In the past，the Colombian government hired peasants and poor farmers to find mines．Many of them died trying to find the well-hidden bombs．
Colombian police official Erick Guzmán hopes the team of rats can come to the rescue．"These rats will be a great help，"he said．
45．How do rats help to find land mines？A
A．By their sense of smell．
B．By their light weight．
C．By their special sight．
D．By their excellent hearing．
46．The advantage of rats over dogs in finding bombs is thatD．
A．they are cleverer
B．they run faster
C．they have a better sense of smell
D．they don't make mines explode as easily
47．The underlined word"They"may refer toC．
A．dogs
B．scientists
C．Wistar rats
D．Méndez and her team
48．What is the text mainly about？B
A．People in Tanzania are suffering from land mines．
B．Specially-trained rats help clear land mines．
C．Dogs are no longer used to find land mines．
D．Land mines have become a great danger to Colombians．
分析 本文叙述了科学家们在哥伦比亚已经训练一组老鼠帮助在农村清除地雷．以前用狗来帮助清除地雷，老鼠的优势是它有灵敏的嗅觉，能够闻出特殊的金属味，并且它们的体重轻引爆地雷的可能性小，还有养它们的费用比养狗的费用低．
解答 45．A 细节理解题．根据第二段的therats can smell special metals in the mines and then signal（发信号） to their human team．老鼠可以闻到地雷中的特殊金属，然后给人发信号，故选A．
46．D 细节理解题．根据第三段的Butrats are much lighter than dogs．They stand less of a chance ofsetting off the mines，但是老鼠比狗更轻．他们的体重轻引爆地雷的可能性小，故选D．
47．C 词义猜测题．根据前面的LuisaFernanda Méndez and her team in Colombia are training the even lighter Wistarrats．These are thewhite rats with red eyes that scientists often use in laboratory experiments．Luisa Fernanda Méndez女士和她的团队在哥伦比亚训练的更轻的Wistar rats，这些红眼睛的小白鼠，科学家们经常在实验室做实验中使用．所以此处指上文提到的Wistar rats，故选C．
48．B 主旨大意题．根据全文的内容可知，主要介绍了受过特殊训练的老鼠帮助人们清理地雷的事，故选B．
点评 本文是科教类阅读，主要考查细节理解题和推理判断题．在做细节理解题时，首先根据题目要求迅速在文章里找出相应的段落、句子或短语．认真比较选项和文中细节的区别，在做推理判断题时不要以个人的主观想象代替文章的事实，要根据文章事实进行合乎逻辑的推理判断．
