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  3. It takes a long time to grow a tree. How long? Well, pine trees are the quickest growing trees, but still, they take twenty year

It takes a long time to grow a tree. How long? Well, pine trees are the quickest growing trees, but still, they take twenty year

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问题     It takes a long time to grow a tree. How long? Well, pine trees are the quickest growing trees, but still, they take twenty years to reach a size suitable for cutting and harvesting. An oak takes about sixty years to grow to a good size. A redwood may take hundreds of years.
    Lumber companies, which make their money on trees, depend on those that grow quickly. Therefore, they are always looking for methods to make trees grow faster. So far, the secret to fast growing trees seems to lie in " super-seeds. " These are seeds that are gathered from the quickest growing trees in a forest. One company searched 100,000 acres of trees and selected the seeds from just fifteen trees. These two ounces of seed were enough to plant several hundred new trees. Eventually, when these trees have grown, seeds will again be taken only from the fastest growing trees of crop. This process of artificial selection will yield, in the future, a super-tree that will grow in half the time it takes normal trees to develop.
    Unfortunately, it takes a long time for a plan like this to reach its goal. The Weyerhauser Lumber Corporation, which started its first collection of seed in 1958, is just now beginning to harvest the super-seeds of the first generation of the faster growing trees.
The word "therefore" in paragraph 2 indicates that a______.
选项 A、speech is beginning
B、conclusion follows
C、comparison is being made
D、metaphor is being used
答案B
解析 第二段。Therefore因此。由于前面提到的原因，才有了后面的行为或决定。这个词的前面通常是原因，该词后则通常是结果。选项B是正确的。
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