Clone Farm Factory farming could soon enter a new era of mass production. Companies in the US are developing the technology needed to 'clone' chickens on a massive scale. Once a chicken with desirable traits has been bred or genetically engineered, tens of thousands of eggs, which will hatch into identical copies, could roll off the production lines every hour. Billions of clones could be produced each year to supply chicken farms with birds that all grow at the same rate, have the same amount of meat and taste the same. This, at least, is the vision of the US's National Institute of Science and Technology, which has given Origen Therapeutics of Burlingame, California, and Embrex of North Carolina $ 4.7 million to help fund research. The prospect has alarmed animal welfare groups, who fear it could increase the suffering of farm birds. That's unlikely to put off the poultry industry, however, which wants disease resistant birds that grow faster on less food. 'Producers would like the same meat quantity but to use reduced inputs to get there. ' says Mike Fitzgerald of Origen. To meet this demand, Origen aims to 'create an animal that is effectively a clone', he says. Normal cloning doesn't work in birds because eggs can't be removed and implanted. Instead, the company is trying to bulk-grow embryonic stem cells taken from fertilized eggs as soon as they're laid. 'The trick is to culture the cells without them starting to distinguish, so they remain pluripotent. ' says Fitzgerald. Using a long-established technique, these donor cells will then be injected into the embryo of a freshly laid, fertilized recipient egg, forming a chick that is a 'chimera'. Strictly speaking, a chimera isn't a clone, because it contains cells from both donor and recipient. But Fitzgerald says it will be enough if, 95 percent of a chicken's body develops from donor cells. 'In the poultry world, it doesn't matter if it's not 100 percent. ' he says. Another challenge for Origen is to scale up production. To do this, it has teamed up with Embrex, which produces machines that can inject vaccines into up to 50,000 eggs an hour. Embrex is now trying to modify the machines to locate the embryo and inject the cells into precisely the right spot without killing it. In future, Origen imagines freezing stem cells from different strains of chicken. If orders come in for a particular strain, millions of eggs could be produced in months or even weeks. At present, maintaining all the varieties the market might call for is too expensive for breeders, and it takes years to bread enough chickens to produce the billions of eggs that farmers need.Which statement is the best description of the new era of factory farming according to the first paragraph?A．Eggs are all genetically engineeredB．Thousands of eggs are produced every hour.C．Cloned chickens are bulk-produced with the same growth rate, weight and taste.D．Identical eggs can be hatched on the production lines.
A.B.7C.D.E.F.G.WhichH.EggsI.ThousandsJ.C．ClonedK.D．Identical
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以下关于缓冲型和非缓冲型冠外附着体的描述，错误的是
A．非缓冲型冠外附着体常需采用两个或多个基牙形成联冠
B．采用缓冲型冠外附着体的义齿戴入后，允许义齿在各方向上有轻微的运动
C．缓冲型冠外附着体能为义齿提供更好支持作用
D．当缺牙区牙槽嵴条件差时，应采用缓冲型冠外附着体
E．缓冲型冠外附着体能减小传递到基牙上的侧方扭力
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