四六级

　　英语六级阅读要靠理解与词汇掌握，我们在做题时，一定要端正心态，不要急躁，先弄清后面的题目内容，了解文章类型，再根据阅读问题有选择性的阅读文章，可以有效提升我们的做题时间与正确率，本文小编为大家整理了一篇阅读，实际操练吧!

　　If you go down to the woods today, you may meet high-tech trees genetically modified to speed their growthor improve the quality of their wood. Genetically-engineered food crops have become increasingly common, albeit controversial. over the past ten years. But genetic engineering of trees has lagged behind.

　　Part of the reason is technical. Understanding. and then altering, the genes of a big pine tree are more complex than creating a better tomato. While tomatoes sprout happily, and rapidly, in the laboratory, growing a whole tree from a single, genetically altered cell in a test tube is a tricky process that takes years, not months. Moreover. little is known about tree genes. Some trees, such as pine trees. have a lot of DNA-roughly ten times as much as human. And, whereas the Human Genome Project is more than half-way throughits task of isolating and sequencing the estimated 100,00 genes in human cells. similar efforts to analyzetree genes are still just saplings (幼苗).

　　Given the large number of tree genes and the little that is known about them, tree engineers are starting with a search for genetic "markers". The first step is to isolate DNA from trees with desirable propertiessuch as insect resistance. The next step is to find stretches of DNA that show the presence of a particular gene. Then, when you mate two trees with different desirable properties, it is simple to check which offspring contain them all by looking for the genetic markers. Henry Amerson, at North Carolina State University, is using genetic markers to breed fungal resistance into southern pines. Billions of these are grown across America for pulp and paper, and outbreaks of disease are expensive. But not all individual trees are susceptible. Dr. Amerson’s group has found markers that distinguish fungus-resistant stock from disease-prone trees.Using traditional breeding techniques, they are introducing the resistance genes into pines on test sites in America.

　　Using generic markers speeds up old-fashioned breeding methods becauseyou no longer have to wait for the tree to grow up to see if it has the desiredtraits. But it is more a sophisticated form of selective breeding. Now. however.interest in genetic tinkering (基因修补) is also gaining ground. To this end, Dr.Amerson and his colleagues are taking part in the Pine Gene Discovery Project. an initiative to identify and sequence the 50,000-odd genes in the pine tree's genome. Knowing which gene does what should make it easier to know what to alter.

　　1. Compared with genetic engineering of food crops, genetic engineering of trees____________________.

　　A) began much later

　　B) has developed more slowly

　　C) is less useful

　　D) was less controversial

　　2. What does the author think about the genetic engineering of pine trees?

　　A) Time-consuming.

　　B) Worthwhile.

　　C) Significant.

　　D) Technically impossible.

　　3. What can we learn about the research on tree genes?

　　A) The research methods are the same as the analysis of human genes.

　　B) The findings are expected to be as fruitful as the analysis of human genes.

　　C) It will take as much time and effort as the analyst, of human genes.

　　D) The research has been mainly concentrated on the genes of young trees.

　　4. It is discovered by Henry Amerson’s team that_______________.

　　A) southern pines cannot resist fungus

　　B) all southern pines are not susceptible

　　C) the genetic marker in southern pines was the easiest to identify

　　D) fungus-resistant genes came originally from outside the U.S.A.

　　5. What is the primary objective of carrying out the Pine Gene Discovery Project?

　　A) To speed up old-Fashioned breeding methods.

　　B) To identify all the genes in the pine tree's genome.

　　C) To find out what desired traits the pine trees have.

　　D) To make it easier to know which gene needs altering.

　　答案：

　　1.相较于粮食作物的基因工程，树木的基因工程______________。

　　A)开始得较晚

　　B)发展得较慢

　　C)用处较小

　　D)争议性较低

　　[B]本文并没有提到树木基因改良技术从什么时候开始，所以有可能树木的基因改良技术和别的基因改良技术在开始的时间上相差不大，但在所取得的成果方面却有很大的差别，因此，本题关键在于理解首段末句中的lag behind指的是程度上的落后，而非时间上的落后，故B正确。

　　2.作者对于松树基因工程怎么看?

　　A)耗时。

　　B)十分值得。

　　C)很重要。

　　D)技术上不可能。

　　[B]第2段第3句中的that takes years表明研究树木的基因改造技术将花费很长时间，因此选项A为本题答案。原文没有就选项B和C两方面做出讨论，因此不能推断出这两个选项;虽然第2段首句提到technical一词，但文章表明树木基因改造技术是可行的。只是会花费较多的时问，因此选项D也不正确。

　　3.对于树木基因进行的研究，我们了解到什么?

　　A)研究方法与分析人类基因时相同。

　　B)人们预计研究成果会与人类基因分析一样硕果累累。

　　C)所花的时间和精力与人类基因分析一样多。

　　D)研究主要关注在小树的基因上面。

　　[A]第2段末句中的similar cfforts指的就是task of isolating and sequencing，即分析基因的常用方法。该句表明人类基因和树种基因的分析方法相同，但进展有差别，因此选项A为正确的推断。

　　4.Henry Amerson的研究小组发现，__________________。

　　A)南部黄松不能抵抗真菌

　　B)并不是所有的南部黄松都很容易染病

　　C)南部黄松的基因标记最容易识别

　　D)有真菌抵抗能力基因源自国外而非美国

　　[B]选项B是一个半否定的句式，因此本题关键在于理解选项B的Al1...are not...结构在意义上等同于第3段倒数第3句的not all... are...。第3段倒数第2句中的fungus-resistant stock指的是南方松树中能抗真菌的树种，并非别的与南方松树毫不相关的树种，因此A的说法不正确。

　　5.开展“松树基因发现项目”的主要目的是什么?

　　A)加快旧式的育种方法。

　　B)识别松树基因组中的所有基因。

　　C)找到松树所具有的优质特点。

　　D)让发现什么基因需要做改变的过程变得更加简单。

　　[B]末段倒数第2句中的an initiative...是the Pine Gene Discovery Project的同位语，表明开展该计划的目的，因此选项B为本题答案。其他选项都是在完成该计划后能够达成的工作，它们都要以松树基因的排列组合为基础，因此，这些选项都不是primary objective，而是在实现了primary objective之后继续进行的工作。

　　以上就是小编为大家介绍的相关信息，希望对大家有帮助。想了解更多四六级备考课程、备考资讯，请点击文都网校四六级资讯站查询!有问题找文都☞☞☞详情咨询入口>>>

     编辑推荐