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  3. In the past oysters were raised in much the same way as dirt fanners raised tomatoes—by transplanting them. First, farmers selec

In the past oysters were raised in much the same way as dirt fanners raised tomatoes—by transplanting them. First, farmers selec

admin2013-01-20  55
问题     In the past oysters were raised in much the same way as dirt fanners raised tomatoes—by transplanting them. First, farmers selected the oyster bed, cleared the bottom of old shells and other remains, and then scattered clean shells about Next they "planted" fertilized oyster eggs, which within two or three weeks hatched into larvae. The larvae drifted until they attached themselves to the clean shells on the bottom. There they remained and in time grew into baby oysters called seed or spat(贝卵). The spat grew larger by drawing in seawater from which they derived microscopic particles of food. Before long, farmers gathered the baby oysters, transplanted them in other waters to speed up their growth, and then transplanted them once more into another body of water to fatten them up.
    Until recently the supply of wild oysters and those crudely farmed were more than enough to satisfy people’s needs. But today the delicious seafood is no longer available in abundance. The problem has become so serious that some oyster beds have vanished entirely.
    Fortunately, as far back as the early 1900’s marine biologists realized that if new measures were not taken, oysters would become extinct or at best a luxury food. So they set up well-quipped hatcheries and went to work. But they did not have the proper equipment or the skill to handle the eggs. They did not know when, what, and how to feed the larvae. And they knew little about the predators that attacked and ate baby oysters by the millions. They failed, but they doggedly (努力) kept at it. Finally, in the 1940’s a significant breakthrough was made.
    The marine biologists discovered that by raising the temperature of the water, they could induce oysters to lay eggs not only in the summer but also in the fall, winter, and spring. Later they developed a technique for feeding the larvae and rearing them to spat Going still further, they succeeded in breeding new strains that were resistant to diseases, grew faster and larger, and flourished in water of different salinities(盐分) and temperatures. In addition, the cultivated oysters tasted better!
At what stage of oysters did farmers begin to speed up their growth and fatten them up in the past?
选项 A、Shell.
B、Egg.
C、Larvae.
D、Spat
答案D
解析 本题考查分析理解能力。The spat grew larger by drawing in seawater from which they derived microscopic particles of food．Before long，farmers gathered the baby oysters，transplanted them in other waters to speed up their growth，and then transplanted them once more into another body of water to fatten them up．
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