If you go down to the woods today, you may meet high-tech trees—genetically modified to speed their growth or 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 halfway through its task of isolating and sequencing the estimated 100,000 genes in human cells, similar efforts to analyze tree genes are still just saplings. 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 properties such 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 genetic markers speeds up old-fashioned breeding methods because you no longer have to wait for the tree to grow up to see if it has the desired traits. But it is more a sophisticated form of selective breeding. Now, however, interest in genetic tinkering 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.

单选题 Compared with genetic engineering of food crops, genetic engineering of trees _____.

【正确答案】 B

【答案解析】解析：事实细节题。由题干中的genetic engineering of trees可定位到第一段最后一句。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，本题关键在于理解第一段最后一句中的lag behind指的是程度上的落后，而非时间上的落后，故B项正确。

单选题 The author thinks that the genetic engineering of pine trees is _____.

单选题 Which of the following can be learned from Paragraph 2 about the research on tree genes?

【正确答案】 A

【答案解析】解析：事实细节题。第二段最后一句中的similar efforts指的就是task of molating 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A项为正确的推断。as much time与原文内容不符；第二段末的saplings虽然是“小树苗”的意思，但是在该句中，saplings用作比喻树种基因研究只处于初级阶段，并非真的是young trees的意思，D项只是从字面上理解saplings一词，不正确。