两个振动完全相同的声源A和B,发声的频率为50Hz,A、B相距10m,声音的传播

题型:填空题

问题:

两个振动完全相同的声源A和B,发声的频率为50Hz,A、B相距10m,声音的传播速度为340m/s,则在A、B连线上距A为______处听不见声音.

考点:波的衍射波的干涉
题型:填空题

相对2002年,2003年实际使用外资金额减少的行业数为()。

A.1个

B.2个

C.3个

D.4个

题型:填空题

阅读理解。

     The greatest recent social changes have been in the lives of women. During the twentieth century there

has been a remarkable shortening of the proportion of a woman's life spent in caring for children. A woman

marrying at the end of the nineteenth century would probably have been in her middle twenties, and would

be likely to have seven or eight children, of whom four or five lived till they were five years old. By the time

the youngest was fifteen, the mother would have been in her early fifties and would expect to live a further

twenty years, during which custom, opportunity and health made it unusual for her to get paid work. Today

women marry younger and have fewer children. Usually a woman's youngest child will be fifteen when she

is forty-five and can be expected to live another thirty-five years and is likely to take paid work until retirement

at sixty. Even while she has the care of children, her work is lightened by household appliances and

convenience food.

     This important change in women's life-pattern has only recently begun to have its full effect on women's

economic position. Even a few years ago most girls left school at the first opportunity, and most of them took

a full-time job. However, when they married, they usually left work at once and never returned to it. Today the

school- leaving age is sixteen, many girls stay at school after that age, and though women tend to marry

younger, more married women stay at work at least until shortly before their first child is born. Very many

more afterwards return to full-time or part-time work. Such changes have led to a new relationship in marriage,

with the husband accepting a greater share of the duties and satisfactions of family life, and with both husband

and wife sharing more equally in providing the money, and running the home, according to their abilities and

interests of each of them.

1. For women during the twentieth century, the amount of time spent taking care of children _____.

A. accounted for a great part of their lives

B. was considered to be surprisingly long

C. was longer than in previous centuries

D. was shorter than in previous centuries

2. According to the passage, around the year 1900 most women married _____.

A. in their early fifties

B. at about twenty-five

C. at any age from fifteen to forty-five

D. soon after they were fifteen

3. When she was over fifty, the late nineteen-century mother _____.

A. was unlikely to find a job even if she wanted one

B. would expect to work until she died

C. was usually expected to die fairly soon

D. would be healthy enough to take up paid employment

4. One reason why the mother of today may take a job is that she _____.

A. can retire from family responsibilities when she reaches sixty

B. need not worry about food for her children

C. is younger when her children are old enough to look after themselves

D. does not like children herself

题型:填空题

政府

题型:填空题

渡船安全检查时间有何规定?

题型:填空题

《消费者权益保护法》中一项最核心的原则是______。

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