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问题 多选题

如图所示的电路中，下列说法正确的是（　　）

A．只闭合开关S2，灯L1和L2串联，电流表测量的是串联电路的电流

B．只闭合开关S1和S3，灯L1和L2并联，电流表测量的是并联电路干路的电流

C．只闭合开关S1和S2，灯L1和L2并联，电流表测量的是灯L2电流

D．闭合开关S1、S2和S3，电流表和电源都可能被烧坏

答案

A、只闭合开关S2，电流依次经过灯L1和L2，则L1和L2串联，电流表测量的是串联电路的电流，故A正确；

B、只闭合开关s1和s3时，电流分别流入灯泡L1和L2，故两灯泡并联，电流表在干路上，测L1、L2的电流之和，故B正确；

C、只闭合开关s1和s2时，对灯L2短路，电流表测通过灯L1的电流，故B错误；

D、闭合开关S1、S2和S3，因电流表相当于导线，会造成电源短路，烧坏电源和电流表，故D正确．

故选ABD．

选择题
若平面向量
a
与
b
=（1，-2）的夹角是180°，且|
a
|=3
5
，则
a
等于（　　）
A．（6，-3）B．（3，-6）C．（-3，6）D．（-6，3）
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单项选择题

In one sense, we can trace all the problems of the American city back (91) a single starting point: we Americans don’t like our cities very much.
That is, on the (92) of it, absurd. After all, more than three-fourths of us now live in cities, and more are (93) to them every year. We are told that the problems of our cities are (94) more attention in Washington, and scholarship has discovered a whole new (95) in urban studies.
(96) , it is historically true: in the American psychology, the city has been a basically suspect institution, (97) with the corruption of Europe, totally lacking that sense of spaciousness and innocence of the (98) and the rural landscape.
I don’t pretend to be a scholar on the history of the city in American life. But my thirteen years in public (99) , first as an officer of the U. S. Department of Justice, then as Congressman, and now as Mayor of the biggest city in America have taught me (100) too well the fact that a p antiurban attitude (101) consistently through the mainstream of American thinking. Much of the (102) behind the settlement of America was in reaction (103) the conditions in European industrial centers and much of the theory (104) the basis of freedom in America was linked directly to the availability of land and the perfectibility of man outside the corrupt influences of the city.
What has this to do with the predicament of the modern city I think it has (105) to do with it. For the fact is that the United States (106) the federal government, which has historically established our national priorities, has simply never thought that the American city was "worthy" of (107) —at least not to the (108) of expending any basic resources on it.
Antipathy to the city predates the American experience. When industrialization (109) the European working man into the major cities of the continent, books and pamphlets appeared (110) the city as a source of crime, corruption, filth, disease, vice, licentiousness, subversion, and high prices.

A．supporting

B．promoting

C．encouraging

D．inspiring
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