更多"Scientists have known for more than"的相关试题:
[单项选择]Scientists have known for more than two decades that cancer is a disease of the genes. Something scrambles the DNA inside a nucleus, and suddenly, instead of dividing in a measured fashion, a cell begins to copy itself furiously. Unlike an ordinary cell, it never, stops. But describing the process isn’t the same as figuring it out. Cancer cells are so radically different from normal ones that it’s almost impossible to untangle the sequence of events that made them that way. So for years researchers have been attacking the problem by taking normal cells and trying to determine what changes will turn them cancerous - always Without success.
According to a report in the current issue of Nature, a team of scientists based at M. I .T.’s Whitehead Institute for Biomedical Research has finally managed to make human ceils malignant -a feat they accomplished with two different cell types by inserting just three altered genes into their DNA. While these manipulations were done only in lab d
A. developing malignant cells in human bodies
B. making normal human cells cancerous
C. controlling the change of human cells
D. changing the genes of cancer cells
[填空题]Scientists have known for decades that coffee beans contain oil. Mohapatra and colleagues, however, were the first to analyze coffee grounds.
Used grounds usually end up in landfills, though gardeners sometimes use them as a kind of fertilizer. The scientists collected used grounds from Starbucks, which gives bags of grounds away as part of the company’s "Grounds for your garden" program.
To prepare the grounds for analysis, the team first dried them in an oven. They mixed the resulting powder with a combination of solvents (溶剂) that caused the oil to separate from the solution. They extracted the oil, saving the solvents for the next round of processing. The remains could still be used as compost, ethanol feedstock, and fuel pellets.
"We’re not wasting anything, " Mohapatra told Discovery News. "It’s a recycling process."
The study showed that used grounds contain about 15 percent oil by weight, depending on the type of coffee. That’s not too f
[单项选择]Just 10 years into a new century, more than two-thirds of the country sees the past decade as a period of decline for the U. S. , according to a new TIME poll that probed Americans on the decade since the tragic events of Sept. 11, 2001. The poll confirms that the country is going through one of its longest sustained periods of unhappiness and pessimism ever. Today’s teenagers hardly remember a time before 9/11, the war on terrorism, the war in Iraq and constant economic upheaval. Baby boomers, the generation known for continuous reinvention, are filled with worry and doubt about their future and the future of their children.
It is hard to overstate what a fundamental change this represents. A country long celebrated for its optimism amid adversity is having trouble finding the pluck and the spirit that have seen it through everything from world wars to nuclear threats to space races. The U
A. arrogant
B. detached
C. involved
D. patriotic
[填空题]More than two million people in Europe now have fibre broadband direct to their home, suggests a survey.
The latest figures on superfast broadband delivered by fibre to the home (FTTH) shows 18% growth over the last survey compiled in late 2008.
The continued growth suggests that the global economic downturn has not hit plans to build a fibre infrastructure (基础设).
Sweden tops the list of nations rolling out the technology, with 10.9% of its broadband customers using fibre.
Karel Helsen, president of Europe’s Fibre-To-The-Home Council, said the growth matched predictions that were revised when the credit crunch (信用紧缩) started to make itself felt.
"The numbers in 2009 are in line with the latest forecasts," said Mr. Helsen.
By 2012, the FTTH Council expects that 13 million people across 35 European nations will have their broadband delivered by fibre. Such services would start at speeds of 100 megabits per second (mbps), said Mr. Helsen.
A
