题目内容
（请给出正确答案）
While______an efficiency test on an engine, certain precautions should be observed.
A．making
B．to make
C．being made
D．made
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更多“While______an efficiency test on an engine, certain precautions should be observed.A．makin”相关的问题
A.A.extravagant
B.B.indispensable
C.C.intermittent
D.D.exquisite
What is the future work planned to do？
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B．To realize full coverage of area the satellite passes over
C．To build more ground observation centers.
D．To compare satellite information with those from ground.
What is the purpose of sub cooling R-12 in the condenser？ .
A.to increase the system efficiency by sensible heat transfer
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A large population in an underdeveloped country may lead to ______.
A．a rise in work efficiency
B．a redaction in average income
C．a decline in grain production
D．a shortage of farm workers
The very core of marketing lies in ______.
A．an understanding of consumer needs
B．the efficient movement of goods
C．developing new wants for consumer goods
D．making goods readily available to customers
The second paragraph uses facts to develop the essential idea that ______.
A．a plant efficiently utilizes most of the water it absorbs
B．carbon dioxide is the essential substance needed for plant development
C．a plant needs more water than is found in its composition
D．the stronger the wind, the more the water vapor loss
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A．a plant efficiently utilizes most of the water it absorbs
B．carbon dioxide is the essential substance needed for plant development
C．a plant needs more water is found in its composition
D．the stronger the wind, the more the water vapor loss
听力原文： (33)Researchers report that doing two or more things at once may decrease efficiency and actually take extra time switching from one task to another. In the most severe cases, it can even mean the difference between life and death.
In the study, four groups of young adults carried out a series of tasks and switched between different tasks, some complicated, such as solving math problems, and some more familiar, such as identifying geometric shapes. (34)The researchers found that time was lost in just switching from one task to another, and that time costs increased with the complexity of the tasks. “For each aspect of human performance—perceiving, thinking and acting people have specific mental resources whose effective use requires supervision through executive mental control,” said the lead author, David Meyer in materials provided with the report.
So-called“ multitasking” is becoming increasingly common because of cell phones and computers. the researchers point out, but it may just be adding wasted time and inefficiency to our days. A mere half second of time lost to task switching can mean the difference between life and death for a driver using a cell phone, Meyer said. (35)The authors say the research should make employers and employees think twice before implementing multitasking.
(30)
A．Multitasking is inefficient and wastes time.
B．Multitasking is a matter of life and death.
C．Multitasking is the process of executive control.
D．Multitasking is becoming increasingly common.
Part B
Copying Birds May Save Aircraft Fuel
Both Boeing and Airbus have trumpeted the efficiency of their newest aircraft, the 787 and A350 respectively. Their clever designs and lightweight composites certainly make a difference. But a group of researchers at Stanford University, led by Ilan Kroo, has suggested that airlines could take a more naturalistic approach to cutting jet-fuel use, and it would not require them to buy new aircraft.
The answer, says Dr Kroo, lies with birds. Since 1914, scientists have known that birds flying in formation—a V-shape—expend less energy. The air flowing over a bird's wings curls upwards behind the wingtips, a phenomenon known as upwash. Other birds flying in the upwash experience reduced drag, and spend less energy propelling themselves. Peter Lissaman, an aeronautics expert who was formerly at Caltech and the University of Southern California, has suggested that a formation of 25 birds might enjoy a range increase of 71 % .
When applied to aircraft, the principles are not substantially different. Dr Kroo and his team modelled what would happen if three passenger jets departing from Los Angeles, San Francisco and Las Vegas were to assemble over Utah, assume an inverted V-formation, occasionally change places so all could have a turn in the most favourable positions, and proceed to London. They found that the aircraft consumed as much as 15% less fuel (coupled with a reduction in carbon-dioxide output). Nitrogen-oxide emissions during the cruising portions of the flight fell by around a quarter.
There are, of course, knots to be worked out. One consideration is safety, or at least the perception of it. Would passengers feel comfortable travelling in companion？ Dr Kroo points out that the aircraft could be separated by several nautical miles, and would not be in the intimate groupings favoured by display teams like the Red Arrows. A passenger peering out of the window might not even see the other planes. Whether the separation distances involved would satisfy air-traffic-control regulations is another matter, although a working group at the International Civil Aviation Organisation has included the possibility of formation flying in a blueprint for new operational guidelines.
It remains to be seen how weather conditions affect the air flows that make formation flight more efficient. In zones of increased turbulence, the planes' wakes will decay more quickly and the effect will diminish. Dr Kroo says this is one of the areas his team will investigate further. It might also be hard for airlines to co-ordinate the departure times and destinations of passenger aircraft in a way that would allow them to gain from formation flight. Cargo aircraft, in contrast, might be easier to reschedule, as might routine military flights.
As it happens, America's armed forces are on the case already. Earlier this year the country's Defence Advanced Research Projects Agency announced plans to pay Boeing to investigate formation flight, thought the programme has yet to begin. There are reports that some military aircraft flew in formation when they were low on fuel during the Second World War, but Dr Lissaman says they are unsubstantiated. "My father was an RAF pilot and my cousin the skipper of a Lancaster lost over Berlin, "he adds. So he should know.
Findings of the Stanford University researchers will promote the sales of new Boeing and Airbus aircraft.
A．True
B．False
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