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在极短时间内，发电机能承受事故不平衡负荷。为了防止负序电流产生的损耗引起转子磁极表面和护环局部过热和烧损。必须严格控制事故不平衡负荷及时间，负序电流的标幺值的平方与事故时间的乘积不大于（），即I22t＜10s（I2为负序电流标幺值，t为事故时间，单位为秒，事故时负序电流的允许值）

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单项选择题

When a disease of epidemic proportions threatens the public, scientists immediately get to work, trying to locate the source of affliction and find ways to combat. Vaccination is one of the effective ways to protect the (1) population of a region or country which may be (2) grave risk. The process of vaccination allows the patient’s body to (3) immunity to the virus or disease so that, if it is encountered, one can fight it (4) naturally. To accomplish this, a small weak or dead (5) of the disease is actually injected into the patient in a controlled environment, (6) his body’s immune system can learn to fight the invader (7) . Information (8) how to penetrate the disease’s defenses is (9) to all elements of the patient’s immune system in a process that occurs naturally, in which genetic information is passed from cell to cell. This makes sure that (10) the patient later come into contact with the real problem, his body is well equipped and trained to (11) with it, having already done so before.

There are, however, dangers (12) in the process. (13) , even the weakened version of the disease contained in the vaccine proves (14) much for the body to handle, resulting in the immune system (15) , and, therefore, the patient’s death. Such is the case of the smallpox vaccine, (16) to eradicate the smallpox epidemic that nearly (17) the whole Native American population and killed massive numbers of settlers. (18) 1 in 10,000 people who receive the vaccine (19) the smallpox disease from the vaccine itself and dies from it. Consequently, the process, which is truly a (20) , may indeed hide some hidden curses.

17（）

A.wiped out

B.ruled out

C.break down

D.died out
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单项选择题

患者在急性DIC时给予的药物治疗，哪项组合是正确的（）

A.早期肝素不应使用

B.应早期使用PAMBA

C.早期应大量使用皮质激素

D.早期可使用抗血小板聚集剂

E.以上都不是
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