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程序设计语言可划分为低级语言和高级语言两大类。与高级语言相比，用低级语言开发的程序，其 (1) ，但在 (2) 的场合，还经常全部或部分地使用低级语言。在低级语言中，汇编语言与机器语言十分接近，它使用了 (3) 来提高程序的可读性。高级语言有很多种类，其中，PROLOG是一种 (4) 型语言，它具有很强的 (5) 能力。 (4)
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编译器和解释器是两种高级语言处理程序，与编译器相比， (1) 。编译器对高级语言源程序的处理过程可以划分为词法分析、语法分析、语义分析、中间代码生成、代码优化、目标代码生成等几个阶段：其中，代码优化和 (2) 并不是每种编译器都必需的。词法分析的作用是识别源程序中的 (3) ；语法分析中的预测分析法是 (4) 的一种语法分析方法：编译器在 (5) 阶段进行表达式的类型检查及类型转换。 (2)
You can find him in the bookstore__________(在《飘》这本书的旁边)．
程序设计语言可划分为低级语言和高级语言两大类。与高级语言相比，用低级语言开发的程序，其 (1) ，但在 (2) 的场合，还经常全部或部分地使用低级语言。在低级语言中，汇编语言与机器语言十分接近，它使用了 (3) 来提高程序的可读性。高级语言有很多种类，其中，PROLOG是一种 (4) 型语言，它具有很强的 (5) 能力。 (3)
There’s a human liver sitting in a lab dish in Madison, Wis. Also a heart, a brain and every bone in the human body even though the contents of the dish are a few cells too small to be seen without a microscope. But these are stem cells, the most immature human cells ever discovered, taken from embryos before they had decided upon their career path in the body. (46) If scientists could only figure out how to give them just the right kick in just the right direction, each could become a liver, a heart, a brain or a bone. (47) When a team from the University of Wisconsin announced their discovery, doctors around the world looked forward to a new era of medicine one without organ-donor shortages or the tissues-rejection problems that bedevil transplant patients today.Doctors also saw obstacles, though. One of them was a U. S. Congress skittish about research on stem cells taken from unwanted human embryos and aborted fetuses. Indeed, 70 lawmakers asked in a firmly worded letter that the Federal Government ban all such work.Yet the era of "grow your own" organs is already upon us, as researchers have sidestepped the stem cell controversy by making clever use of ordinary cells. Today a machinist in Massachusetts is using his own cells to grow a new thumb after he lost part of his chest wall in an accident. A teenager born without half of his chest wall is growing a new cage of bone and cartilage within his chest cavity. Scientists announced that bladders, grown from bladder cells in a lab, have been implanted in dogs and are working. Meanwhile, patches of skin, the first "tissue-engineered" organ to be approved by the U. S. Food and Drug Administration, are healing sores and skin ulcers on hundreds of patients across the U. S.How have scientists managed to do all this without those protean stem cells Part of the answer is smart engineering. (48) Using materials such as polymers with pores no wider than a toothbrush bristle, researchers have learned to sculpt scaffolds in shapes into which cells can settle. The other part of the answer is just plain cell biology. (49) Scientists have discovered that they don’t have to teach old cells new tricks; given the right framework and the right nutrients, cells will organize themselves into real tissues as the scaffolds dissolve. "I’m a great believer in the cells. They’re not just lying there, looking stupidly at each other," says Francois Auger, an infectious disease specialist and builder of artificial blood vessels at Laval University in Quebec City. "They will do the work for you if you treat them right."Replacement hearts—or even replacement heart parts—are at least a decade off, estimates Kiki Hellman, who monitors tissue-engineering efforts for the FDA. "Any problem that requires lots of cell types ’talking’ to one another is really hard," she notes. Bone and cartilage efforts are much closer to fruition, and could be ready for human trials within two years. (50) And what of those magical stem cells that can grow into any organ you happen to need—if the law and biologists’ knowledge permit "Using them," says Sefton, "is really the Holy Grail.\ And what of those magical stem cells that can grow into any organ you happen to need—if the law and biologists’ knowledge permit
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