To solve the size problem of cell phones, scientists have been researching_________

N] [NG]

declining a job. You should write at least 150 words according to the outline given below in Chinese:

1.对公司提供职位表示感谢

2. 解释为何不能接受所提供的职位

3.希望予以谅解，并表达对公司的良好祝愿

A Letter Declining a Job Offer

amount of money within a community?

eed 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&39;s genome. Knowing which gene does what should make it easier to know what to alter.

测试题

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

A.introduce their findings about Venus

B.promote the exploration of Venus

C.convince others that there used to be lives on Venus

D.criticize omer scientists that they are narrow-minded

ulfur. heaved from ancient volcanoes and feeding acid clouds above. Although the second planet is a step farther from the sunthan Mercury, a runaway greenhouse effect makes it hotter indeed. It&39;s the hottest of the nine plants, a toasty 900 degrees Fahrenheit of baking rocky flats from equator to poles. All this under a crushing atmospheric pressure 90 times that of where you&39;re sitting now. From the earthly perspective, a dead end. It must be lifeless.

"Venus has nothing," is the blunt word from planetologist Kevin Zahnle of NASA Ames Research Center in California&39;s Silicon Valley. "We&39;ve written it off. "

Yet a small group of advanced life-forms on Earth begs to differ. and theorizes that bizarre microbial ecosystems might have once populated Venus and. in fact. may be there still. Members of this loose band of researchers suggest that their colleagues have water too much on the brain, and are, in a sense, H2O chauvinists（盲目的爱国者）．

"Astrobiologists are neglecting Venus due more io narrow thinking than actual knowledge of the environment,or environments. where life can thrive." says Dirk Schulze-Makuch, a geobiologist at the University of Texas at El Paso who recently co-authored a Venus-boosting paper in Astrobiology wich colleague Louis Irwin.

The bias against life on Venus is partly rooted in our own biology. Human experience instructs that liquidwater, preferably lot of it. is essential for life. In search for extraterrestrial life, we obsess over small rivers in Mars&39; surface apparently carved by ancient gushes of water. and delight in hints of permafrost (永久冻结带) just underneath its surface. (By comparison. Venus isn&39;t even that interesting to look at:A boring cue ball (台球的白色母球) for backyard astronomers, its clouds reflects 75% of visible light.) Attention and then funding follow the water: Three more landers will depart for Mars this spring. and serious plans for sample-return missions hover in the midterm future.

"If you have limited resources, you base exploration on what you know." says Arizona State University planetary geologist Ronal Greeley. It&39;s like losing your keys on the way home al night: The first place you look is under the streetlights not because they&39;re more likely to be there. but because if they are. you’llspot them. For astrobiologists. the streetlights are the spectral (光谱的) lines for water. and they&39;ve spotted that potential on Mars, Jupiter&39;s moon Europa. even Neptune&39;s moon Triton. Not on the baking rocky flats of Venus.

测试题

Venus is the hottest of all the nine planets in the solar system because_____________.

A.it is not so close to the sun as Mercury

B.many volcanoes spread the whole planet

C.it is covered by a thick layer of cloud

D.greenhouse effect is uncontrollable on it