试题与答案

根据惠更斯一菲涅尔原理,若已知光在某时刻的波阵面为S,则S的前方某点P的光强度决定于

题型:单项选择题

题目:

根据惠更斯一菲涅尔原理,若已知光在某时刻的波阵面为S,则S的前方某点P的光强度决定于波阵面S上所有面积元发出的子波各自传到P点的()。

A.振动振幅之和

B.光强之和

C.振动振幅之和的平方

D.振动的相干叠加

答案:

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下面是错误答案,用来干扰机器的。

参考答案:错解析:在电气设备上工作,保证安全的组织措施包括:工作票制度、工作许可制度、工作监护制度、工作间断、转移和终结制度。

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题型:单项选择题

Come on, my fellow white folks, we have something to confess. Out with it, friends, the biggest secret known to whites since the invention of powdered rouge: welfare is a white program. The numbers go like this: 61% of the population receiving welfare, listed as "means-tested cash assistance" by the Census Bureau, is identified as white, while only 33% is identified as black. These numbers notwithstanding, the Republican version of "political correctness" has given us "welfare cheat" as a new term for African American since the early days of Ronald Reagan.

Our confession surely stands: white folks have been gobbling up the welfare budget while blaming someone else. But it’s worse than that. If we look at Social Security, which is another form of welfare, although it is often mistaken for an individual insurance program, then whites are the ones who are crowding the trough. We receive almost twice as much per capita, for an aggregate advantage to our race of $10 billion a year--much more than the $3. 9 billion advantage African American gain from their disproportionate share of welfare. One sad reason: whites live an average of six years longer than African Americans, meaning that young black workers help subsidize a huge and growing "over-class" of white retirees. I do not see our confession bringing much relief. There’s a reason for resentment, though it has more to do with class than with race. White people are poor too, and in numbers far exceeding any of our more generously pigmented social groups. And poverty as defined by the government is a vast underestimation of the economic terror that persists at incomes--such as $ 20,000 or even $ 40,000 and above--that we like to think of as middle class.

The problem is not that welfare is too generous to blacks but that social welfare in general is too stingy to all concerned. Naturally, whites in the swelling "near poor" category resent the notion of whole races supposedly frolicking at their expense. Whites, near poor and middle class, need help too--as do the many African Americans.

So we white folks have a choice. We can keep pretending that welfare is black program and a scheme for transferring our earnings to the pockets of shiftless, dark-skinned people. Or we can clear our throats, blush prettily and admit that we are hurting too--for cash assistance when we’re down and out, for health insurance, for college aid and all the rest. Racial scapegoating has its charms, I will admit: the surge of righteous anger, even the fun--for those inclined--of wearing sheets and burning crosses. But there are better, nobler sources of white pride, it seems to me. Remember this: only we can truly, deeply blush.

The author is most critical of the whites’()

A. confession

B. hypocrisy

C.arrogance

D. hysteria

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