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  3. An eagle wheels overhead against a crystalline blue sky, Martin Flanagan wal

An eagle wheels overhead against a crystalline blue sky, Martin Flanagan wal

游客2024-08-17  50
问题     An eagle wheels overhead against a crystalline blue sky, Martin Flanagan walks toward a grove of towering cottonwood trees beside the Yellowstone River, which is the color of chocolate milk due to the spring rain.
    As Mr. Flanagan leaves the glaring sun of the prairie and enters the shady grove, his eyes search for a specific tree. As he reaches a narrow-leaf cottonwood, a towering giant, he cranes his neck to look at the top. "This is the one I plan to nominate for state champion," he says, petting the bark with his hand. "It’s beautiful isn’t it?"
    When Europeans first came to North America, one of the largest primeval forests in the world covered much of the continent. Experts say a squirrel could have traveled from the Atlantic coast to the Mississippi River without touching the ground. But only about 3 percent of America’s native old-growth forest remains, and many of the trees they hold are those that were not big enough to attract a logger’s eyes. The result is a generation of trees that barely resemble the native forests that once covered the country.
    That makes some scientists suspect that the surviving forests have lost much of their genetic quality, the molecular muscle that made them dominate the landscape. When the loggers swept through, these scientists say, only poor specimens were left to reproduce. Other researchers wonder whether environmental factors or just plain luck may explain a good part of the supertrees’ success.
    To answer those questions, the mightiest trees of their types, or genetically identical offspring, must be preserved for study, and that is what is being done by a handful of enthusiasts, including Mr. Flanagan and David Milarch, a nurseryman from Copemish, Mich. They are searching out the largest tree of each species and taking cuttings of new growth to make copies of genetic clones of the giants. With tissue culture and grafting, they have reproduced 52 of the 827 living giants and are planning the offspring in what they call "living libraries." More than 20,000 offspring have been planted.
Directions: Complete the following sentences with information given in the passage in a maximum of 10 words for each blank. [br] One of the reasons why the supertrees disappeared was that______.
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答案 loggers tended to cut down the giant trees
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