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But fishing out the largest fish from a population has an unwanted effect: Over time, fewer adult fish get really big. If only the smaller fish reproduce（繁殖）, then future generations become smaller. This is an example of evolution（进化） in action.
One scientist, Dr David Conover has spent the last decade studying the effects of the “keep the big ones” rule and if they can be reversed（颠倒）.
To set up his experiment, Conover and his team caught hundreds of silverside fish and divided them into six groups. For two groups, Conover followed the “keep the large ones” rule and took out the biggest fish. For two other groups, he removed only the small fish.
For the last two groups, he removed fish at random (随意的).
After five years, he measured the fish in each group. In the two groups where the largest fish were regularly removed, the average fish size was smaller than the average size in the other groups. Here was evolution in action: If only small fish survive to reproduce, then future generations of fish will also tend to be small.
For the second five years of his experiment, Conover changed the rules and took fish randomly from each group. At the end of the experiment, he found that the fish that were in the “keep the large ones” group for the first five years had started to get larger again, although he calculated it would take at least 12 years for the fish in that group to return to their original size.
In other words, it takes less time to shrink(变小) than it does to recover.
小题1: The underlined word “it” (Line 2) refers to “ ”
| A．the activity | B．the fish |
| C．the rule | D．the fisherman |
| A．It helps to protect fish numbers. |
| B．It helps to protect fish size. |
| C．It is the custom in most countries. |
| D．They will be punished if they don’t. |
| A．The “keep the big ones” rule made no difference to fish size. |
| B．The “keep the big ones” rule made fish smaller on average. |
| C．The “keep the big ones” rule made the fish bigger on average. |
| D．The “keep the big ones” rule affected all fish populations in the same way. |
| A．To encourage people to fish more carefully. |
| B．To urge governments to change the rules of fishing. |
| C．To describe the results of a scientific experiment. |
| D．To introduce the rules of fishing to readers. |
完形填空
One day a little boy came into a shop. 1 had five dollars and wanted to 2 some pears. He said to the shopkeeper, “Please give me pears for five dollars.”
When the shopkeeper gave him the pears, the boy counted(数)them. Then he said, “Last week my mother bought pears here for five dollars, and she got 3 than I got for five dollars. Why did you give me so 4 ?”
“Don't ask questions, my boy. I have 5 time for questions.”
“Excuse me, sir,” said the little boy,“but...”
“That's all right, my boy,” said the shopkeeper. “Don't you understand? You get fewer pears, and then you will 6 less fruit.”
“All right,” said the boy and he put 7 dollars on the counter. He was going to leave the shop when he heard the words: “Come back! You 8 give me five dollars!”
“That's all right!” said the boy. “Don't you understand? You get 9 dollars, and then you will count less 10 .”
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B. more
C. fewer
D. the fewest
| 阅读下面短文，掌握大意，然后从A、B、C、D四个选项中选出最佳选项。 | ||||
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Life in the 2020s will be very different from life today. Between then and now many changes, will take | ||||
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