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当前学科：高级电气试验工
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对额定频率50Hz的变压器，施加相当于2倍试品额定电压的试验电压来进行感应耐压试验时，试验电源的频率不得低于（）。
A . 75Hz；
B . 100Hz；
C . 150Hz；
D . 200Hz。
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Marriage Advertisements in India Every Sunday morning millions of Indians settle down with a cup of tea and special weekend issues of their newspapers, just as Americans do. But here, with the marriage season approaching, many of them quickly to a Sunday feature that is particularly Indian-the-columns of marriage advertisements in which young people look for husbands and wives. This is relatively modern change in the age-old custom of the arranged marriage. The thousands of advertisements published each week increasingly reflect social changes that coming to this traditional society. For example, although women are still described in terms of appearance, or skill in "the wifely arts", information about her earning power is entering more and more of the advertisements. This reflects the arrival in India of the working wife. Divorce, which used to be almost unheard of in India, is sometimes now mentioned in the advertisements as in the case of a woman whose advertisement in New Delhi newspaper explained that had been "the innocent party" when her marriage broke up. Because the custom of the dowry (marriage payment) is now illegal, some advertisements say "no dowry" or "simple marriage", which means the same thing. However, the fathers of many bridegrooms still require it. In a land where light skin is often regarded as socially preferable, many also require that a woman have a "wheat-color" complexion or that a man be "tall, fair and handsome". Advertisements are placed and eagerly read by a wide range of people in the upper classes, mostly in cities. Many of them receive dozens of answers."There's nothing embarrassing about it," explained a Calcutta businessman advertising a son-in-law. "It's just another way of broadening the contacts and increasing the possibility of doing the contacts and increasing the possibilities of doing the best one for one's daughter." Because of high unemployment and a generally poor standard of living here, one of the best attractions a marriage advertisement can offer is a permit to live abroad, especially in Canada or the United States. A person who has one can get what he wants. One recent Sunday in Madras, for example, a Punjabi engineer living in San Francisco advertised for a "beautiful slim bride with lovely features knowing music and dance". And a man whose advertisement said that he held an American immigration permit was able to say, only girls from rich, well-connected families need apply. The word "dowry" in the third paragraph means marriage payment.（）
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