单选题Since Jonas Salk came up with his polio vaccine, infantile paralysis has virtually disappeared from the United States.

单选题It will be emphasized that commercial space operations are inherently complex, longterm, capital-hungry, and set by a variety of risks.

单选题It's apparent that the wooden bridge is not strong enough to ______ the weight of a lorry.

单选题The professor is quite difficult pleased.

单选题About fifty years ago, plant physiologists set out to grow roots by themselves in solutions in laboratory flasks. The scientists found that the nutrition of isolated roots was quite simple. They required sugar and the usual minerals and vitamins. However, they did not require organic nitrogen compounds. These roots got along fine on mineral inorganic nitrogen. Roots are capable of making their own proteins and other organic compounds. These activities by roots require energy, of course: The process of respiration uses sugar to make the high energy compound ATP, which drives the biochemical reactions. Respiration also requires oxygen. Highly active roots require a good deal of oxygen. The study of isolated roots has provided an understanding of the relationship between shoots and roots in intact plants. The leaves of the shoots provide the roots with sugar and vitamins, and the roots provide the shoots with water and minerals. In addition, roots can provide the shoots with organic nitrogen compounds. This comes in handy for the growth of buds in the early spring when leaves are not yet functioning. Once leaves begin photosynthesizing, they produce protein, but only mature leaves can "export" protein to the rest of the plant in the form of amino acids.

单选题This pair of shoes isn't good, but that pair is______better.

单选题My parents moved out of their old home sometime last year after they had celebrated their 50th {{U}}year{{/U}} there.

单选题 With 2005 fast becoming "the year of the natural disaster", it is time to reflect on how engineering, science and technology can play their fullest part in protecting the planet. Long before the Asian tsunami struck, the science community predicted the particular region of Indonesia to be hit by the next big earthquake; and the engineering and technology community had developed early warning systems costing only ＄ 30 million. But no government in the region heeded the warnings and no early warning systems were in place. We ignored technology of the advance warnings at our peril of 100,000 victims of the tsunami. Governments are not alone in ignoring the views of their scientific community; the public too has its doubts. Part of the reason for this lack of confidence must be down to the failure to engage them in a meaningful way about their concerns. Trust is a two-way street. Instead of claiming that everything would be rosy in the scientific garden "if only the public understood", we must work hard to explore concerns, discover fears and delve deep into the depths of public perceptions. We are getting there. There is a growing realization that effective public engagement is of far greater value than banging the "public understanding" drum. There are still doubters, of course, and sadly their cause is helped whenever they come across opinions presented as fact. All of us must guard against this debilitating practice. In time, effective public engagement should help deliver improved trust as well as better policy, which -- in turn -- might make it more difficult for scientists' warnings to be ignored. Today's technology community is a triumph of international collaboration where engineers and scientists combine to develop solutions to our biggest problems. Of course, technology cannot stop natural disasters but it can mitigate their impact. We are able to identify the birds affected by avian flu. We can chart their migration patterns around the world. We have the means to pursue vaccines. And we have the communication channels to keep people informed. Extolling the virtues of technology is not to pretend technology is perfect in every regard. Far from it. The profligate and unsustainable use of technology in energy and transport has contributed to climate change. But that doesn't mean technology has failed us. We must never lose sight of the fact that technology itself will deliver the solutions to the very problems it can create. If we do, technology will remain sidelined and undervalued, and this major social failure will progressively disadvantage us all. Our vision is of a society embracing technology as a weapon of both progress and defense. Since the beginning of civilization, we have relied on it and enjoyed its benefits -- and most new technologies have had hugely beneficial effects for most people. But now, in an age when the death toll from natural disasters is increasing year on year, with more people living in danger zones, it is ever more urgent that we rely on science and technology to warn us of the dangers to come and provide the solutions we need.

单选题His thoughts were ______ from the painful topic by the sudden arrival of a close friend.

单选题Our plan didn't get up the ground because no one could come.

单选题Most nurses are women, but in the higher ranks of the medical profession women are a A. scarcity B. minority C. minimum D. shortage

单选题As a general rule . September is the worst month of the year for hurricanes in the Gulf.

单选题Double Eagle II, the first trans-Atlantic balloon, was greeted by avid crowds in France.

单选题Because of the bombing that killed six people, Washington has been urging the spokesman to ______ terrorism more severely. A. charge B. censor C. blame D. denounce

单选题Western art of______19th century shows______influence of______Far East.

单选题The doctor preferred to resign rather than be accused publicly of infamous conduct.

单选题You're been so helpful! How can I make up to you?

单选题The mouth is______intelligent than the ears, for they are both controlled by the brain.

单选题Many students today display a disturbing willingness to choose institutions and careers on the basis of earning potential.

单选题We were working ______ time to get everything ready for the exhibition. A. against B. in C. on D. ahead