更多"For millions of years before the ap"的相关试题:
[单项选择]For millions of years before the appearance of the electric light, shift work, allnight cable TV and the Internet, Earth’s creatures evolved on a planet with predictable and reassuring 24-hour rhythms. Our biological clocks are set for this daily cycle. Simply put, our bodies want to sleep at night and be awake during the day. Most women and men need between eight and eight and a half hours of sleep a night to function properly throughout their lives. (Contrary to popular belief, humans don’t need less sleep as they age.)
But on average, Americans sleep only about seven and a half hours per night, a marked drop from the nine hours they averaged in 1910. What’s worse, nearly one third of all Americans get less than six hours of sleep on a typical work night. For most people, that’s not nearly enough.
Finding ways to get more and better Sleep can be a challenge. Scientists have identified more than 80 different sleep disorders. Some sleeping disorders are genetic. But many prob
A. Most people need less sleep when they grow older.
B. Most people need seven and a half hours of sleep every night.
C. On average, people in the U.S. today sleep less per night than they used to.
D. For most people, less than six hours of sleep on a typical work night is enoug
[单项选择]
Learning how to fly took nature millions of years of trial and error—but a winged robot has crackedit in only a few hours, using the same evolutionary principles. Krister Wolff and Peter Nordin of Chalmers University of Technology (CUT) in Gothenburg, Sweden, built a winged robot and set about testing whether it could learn to fly by itself, without any pre-programmed data on what flapping is or how to do it.
To begin with, the robot just twitched and jerked erratically. But, gradually, it made movements that gained height. At first, it cheated—simply standing on its wing tips was one early short cut. After three hours, however, the robot abandoned such methods in favor of a more effective flapping technique where it rotated its wings through 90 degrees and raised them before twisting them back to the horizontal and pushing down.
"This tells us that this kind of evolution is capable of coming up with flying motion," says Peter Bentley, who wo
A. The winged robot could never really fly.
B. The winged robot did not have a motor.
C. The winged robot should go through further evolution before it could fly.
D. The robot could fly if it were lighter.
[单项选择]()from other continents for millions of years, Australia has varieties of species which can hardly be found in other parts of the world.
A. Being separated
B. Having been separated
C. To be separated
D. To have been separated
[填空题]For millions of years, the changes in Earth’s climate have been driven by forces of nature. But for the last century and a half, Earth’s average temperature has been rising (47) than any time in the past ten thou- sand years. The (48) in science is that much of that change has been driven by us.
The climate is not what it used to be. It’s not your grandfather’s climate anymore.
The (49) are everywhere: droughts in the American Southwest and Africa’s Sahara(撒哈拉), (50) seas in Louisiana and Bangladesh (孟加拉国), tropical diseases spreading north and extremes of weather from Florida to France.
There are people who still say global warming needn’t (51) us. If it’s happening at all, it’s a natural trend, not much we can do about it. But there is now hard (52) which shows that the warming is not only real. It’s (53) . It’s altering the climate’s most basic elements like rainfall and evaporation, days of