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问题 选择题

图中两条平行虚线之间存在匀强磁场，虚线间的距离为L，磁场方向垂直纸面向里．abcd是位于纸面内的直角梯形线圈，ab与dc间的距离也为L，t=0时刻ab边与磁场区域边界重合，如图所示，现令线圈以恒定的速度v沿垂直于磁场区域边界的方向穿过磁场区域．取沿a→d→c→b→a的感应电流为正，则在线圈穿越磁场区域的过程中，感应电流I随时间t变化的图线可能是（　　）

A．

B．

C．

D．

答案

开始ab边进入磁场切割磁感线，由右手定则可知，电流方向为a→d→c→b→a，电流方向是正的，故BD错误；

由右手定则可知，ab边离开磁场时，感应电流方向是a→b→c→d→a，电流方向是负的，故A正确，C错误；

故选A．

单项选择题

指导与领导工作越是能使全体人员明确理解组织的目标，则人们为实现组织目标所做的贡献就会越大，这个原理是指导与领导工作原理中的（）

A.指明目标原理

B.命令一致原理

C.目标协调原理

D.直接管理原理
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单项选择题

Most people would be (1) by the high quality of medicine (2) to most Americans. There is a lot of specialization, a great deal of (3) to the individual, a (4) amount of advanced technical equipment, and (5) effort not to make mistakes because of the financial risk which doctors and hospitals must (6) in the courts if they (7) things badly.

But the Americans are in a mess. The problem is the way in (8) health care is organized and (9) . (10) to pubic belief it is not just a free competition system. The private system has been joined a large public system, because private care was simply not (11) the less fortunate and the elderly.

But even with this huge public part of the system, (12) this year will eat up 84.5 billion dollars—more than 10 percent of the U. S. Budget—large number of Americans are left (13) . These include about half the 11 million unemployed and those who fail to meet the strict limits (14) income fixed by a government trying to make savings where it can.

The basic problem, however, is that there is no central control (15) the health system. There is no (16) to what doctors and hospitals charge for their services, other than what the public is able to pay. The number of doctors has shot up and prices have climbed. When faced with toothache, a sick child, or a heart attack, all the unfortunate persons concerned can do is (17) up. Two thirds of the population (18) covered by medical insurance. Doctors charge as much as they want (19) that the insurance company will pay the bill.

The rising cost of medicine in the U. S. A. is among the most worrying problems facing the country. In 1981 the country’s health bill climbed 15.9 percent--about twice as fast as prices (20) general.

4（）

A.countless

B.titanic

C.broad

D.vast
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