若│x+2│+（y-3）2=0,则xy=____

【中美关系从对抗走向正常化】

       材料一 假手蒋介石（美国支持蒋介石发动内战），他们不仅能开辟巨大的中国市场，一个多世纪以来美国商人梦寐以求的市场终于要成为现实了，10亿亚洲主顾会大有助于避免另一次经济危机。……也正是基于独占中国市场的强烈欲望，美国积极支持蒋介石于二战结束不久，发动了全面内战。……（但后来他们支持的蒋介石集团被 * * 党领导的人民解放军打败了）。 ——《中外历史问题八人谈》

       材料二 1960年美国中央情报局外国研究机构康伦公司在《美国对亚洲的外交政策》的报告中说：中国“在过去的10年中几乎在所有（与美国）的较量中取得了胜利”。正是在这种情况下，加上美国的霸权地位（因苏联的争夺和深陷越南战争的泥潭之中）已无可挽回地（在二十世纪七十年代初）处于相对衰弱之中。——《中外历史问题八人谈》

       材料三 2009年1月1日，中美两国领导人互致贺电，热烈庆贺两国建交30周年。30年前，中美正式建立外交关系，由此揭开了两国关系的新篇章，对国际形势和世界格局产生了重大深远的影响。

阅读上述材料，请回答：

（1）结合材料一和所学知识说明：建国初期美国为什么要敌视新中国？为此它采取了哪些敌视政策？举一例说明二十世纪五十年代中国在与美国的较量中取得的重大胜利。

                                                                                                                                                             

                                                                                                                                                             

（2）结合材料二和所学知识说明：二十世纪七十年代美国为什么要改善与中国的关系？请谈谈这一时期中美关系走向正常化的大事。

                                                                                                                                                            

                                                                                                                                                            

                                                                                                                                                            

（3）在二十世纪七十年代中美关系走向正常化的过程中，中美双方发表了哪两份公报？这两份公报表明了中国在台湾问题上的原则立场是什么？

                                                                                                                                                             

（4）在谈到中美关系时，有同学认为美国常给中国制造麻烦，我们不应该和美国建立外交关系；还有同学认为中美之间虽然有矛盾和斗争，但有更广泛的合作领域，应该增进了解，扩大共识，发展建设性合作关系。对此简要谈谈你的认识。

                                                                                                                                                            

                                                                                                                                                            

                                                                                                                                                            

下列哪项不是张力性气胸的临床表现（）

A.呼吸困难

B.心动过速

C.发绀

D.血压升高

E.患侧呼吸音减弱或消失

实体是信息世界中广泛使用的一个术语，它用于表示

A．有生命的事物

B．无生命的事物

C．实际存在的事物

D．一切事物

Questions 51-55 are based on the following passage.

To Err is Human

by Lewis Thomas
Everyone must have had at least one personal experience with a computer error by this time. Bank balances are suddenly reported to have jumped from $ 379 into the millions, appeals for charitable contributions are mailed over and over to people with crazy sounding names at your address, department stores send the wrong bills, utility companies write that they’re turning everything off, that sort of thing. If you manage to get in touch with someone and complain, you then get instantaneously typed, guilty letters from the same computer, saying, "Our computer was in error, and an adjustment is being made in your account."
These are supposed to be the sheerest, blindest accidents. Mistakes are not believed to be the normal behavior of a good machine. If things go wrong, it must be a personal, human error, the result of fingering, tampering a button getting stuck, someone hitting the wrong key. The computer, at its normal best, is infallible.
I wonder whether this can be true. After all, the whole point of computers is that they represent an extension of the human brain, vastly improved upon but nonetheless human, superhuman maybe. A good computer can think clearly and quickly enough to beat you at chess, and some of them have even been programmed to write obscure verse. They can do anything we can do, and more besides.
It is not yet known whether a computer has its own consciousness, and it would be hard to find out about this. When you walk into one of those great halls now built for the huge machines, and standing listening, it is easy to imagine that the faint, distant noises are the sound of thinking, and the turning of the spools gives them the look of wild creatures rolling their eyes in the effort to concentrate, choking with information. But real thinking, and dreaming, are other matters. On the other hand, the evidence of something like an unconscious, equivalent to ours, are all around, in every mail. As extensions of the human brain, they have been constructed the same property of error, spontaneous, uncontrolled, and rich in possibilities.

The author uses his hypothesis that "computers represents an extension of the human brain" in order to indicate that ______.

A. human beings are not infallible, nor are computers
B. computers are bound to make as many errors as human beings
C. errors made by computers can be avoided the same as human mistakes can be avoided
D. computers axe made by human beings and so are their errors

汽轮机盘车过程中，为什么要投入油泵联锁开关？