There Pictures from outer space now
show us how much land has changed on earth. These images are taken by Landsat 7,
a government satellite. The satellites have been used for 27 years. They reveal
the clear-cutting of forests in the northwestern part of the United States.
Pictures show the loss of rain forests in South America. NASA’s Darrel Williams speaks about the Landsat 7 Project. He said that an eruption caused trees to bum up in a large forest. Fifteen years later, pinkish images from space show that the trees and plant life are growing again. Williams says that clear-cut areas easily show up in the pictures. He wants Americans to look at how much land is being cleared of forests in our country. Satellites have provided other information about changes on earth. In the past ten years, more than four miles have shrunk A. sightseers have noted the changes B. computer-animated views have shown the shrinkage C. one of the glaciers was hit by a ship D. the temperatures are much colder [单项选择]Let us now see how randomization is done when a collision occurs. After a ______, time is divided into discrete slots whose length is equal to the worst-case round-trip propagation time on the ether (2t). To accommodate the longest path allowed by Ethernet, the slot tome has been set t0 512 bit times, or 51.2μsec.A.datagram B.collision C.connection D.service
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Sleep Now, Remember Later How sleep helps US consolidate memories is still largely a mystery. A recent study from the University of Liibeck, in Germany, offers one clue-Subjects were given a list of 46 word pairs to memorize, just before sleep. Then when they reached the deepest stages of sleep, electrical currents were sent through electrodes on their" heads to induce very slow brain waves. Such slow waves were induced at random in the brains of one group of subjects, but not another. The next morning, the slow-wave group had better recall of the words. Other types of memory were no| improved, and inducing the slow waves later in the night did not have the same eftect. Why and how the slow waves improved memory is not yet understood, but they are thought to alter the strengths of chemical connections, or synapses, between specific pairs of nerve cells in the brain. Memories are "stored" in these synapses: changing the strength of th A. they can change the strengths of chemical connections in the synapses. B. they can improve the brain’s ability to store memories. C. they can produce new nerve cells in the brain. D. they can activate the nerve cells that are not workin 我来回答: 提交
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