单项选择题

This doesn’t mean that wind and solar, which currently provide less than 1 percent of the world’s primary energy, will replace fossil fuels, which provide 82 percent. In fact, while companies like BP and Shell are cutting back on commercial projects in wind and solar, Big Oil is taking a closer look at how they might be used to increase efficiency internally, or to flee up increasingly profitable fossil fuels, like natural gas, for commercial sale. For example. Valero is building windmills to power refineries, and Chevron is using solar power to make steam to extract tough-to-reach oil. When you consider that the top 15 oil and gas companies have a market capitalization of $1.9 trillion, it’s clear that these firms themselves have the potential to be major renewable customers.
Big oil is thinking of using wind and solar

A. to free up fossil fuels for commercial sale.
B. to replace fossil fuels for commercial sale.
C. to increase efficiency of fossil fuels use.
D. to reduce harm to the environment.
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Most viruses that cause swine flu or bird flu are very hard to pass from one human to another: they don’t cause epidemics. Sometimes, however, further changes in genes create a virus that can spread rapidly among humans, and can produce a more severe illness. One reason this illness is more severe is that the virus is so new. The regular flu that comes each year is caused by a regular human influenza virus that often has similarities to the viruses that have caused the nu in years past, so people have some degree of immunity to the latest virus. The unusual swine flu or bird flu viruses that develop the ability for person-to-person spread are so different that people have little or no immunity to them. What is the main reason that the swine flu is very dangerous to humans A. That it is fatal and has killed many. B That it has spread to many countries. C. That people know nothing about it. D. That people have no immunity to it.
Most viruses that cause swine flu or bird flu are very hard to pass from one human to another: they don’t cause epidemics. Sometimes, however, further changes in genes create a virus that can spread rapidly among humans, and can produce a more severe illness. One reason this illness is more severe is that the virus is so new. The regular flu that comes each year is caused by a regular human influenza virus that often has similarities to the viruses that have caused the nu in years past, so people have some degree of immunity to the latest virus. The unusual swine flu or bird flu viruses that develop the ability for person-to-person spread are so different that people have little or no immunity to them.
What is the main reason that the swine flu is very dangerous to humans
A. That it is fatal and has killed many. B That it has spread to many countries.
C. That people know nothing about it. D. That people have no immunity to it.
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For example, those that had learned the maze six weeks after the injection had three times as much activity in their stained cells as those mice that learned the maze eight weeks after injection, when the stained cells were fully mature. Cells examined at less than six weeks’ old at the time of learning did not show as much activity as at six weeks, however. According to Frankland, this suggests that when neurons reach six weeks of age they are specifically recruited to form the brain networks that support new memories. According to Fankland, the example shows that neurons in mice’s brains are specially recmited When
A. they are six weeks old.
B. they are eight weeks old.
C. they are between six and eight weeks old.
D. they are less than six weeks ol
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