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问题 单项选择题

设X～N(μ，0.362)，从中抽取容量为9的一个样本，其样本的均值为，则总体均值μ的置信度为0.95的置信区间为()。

A.A

B.B

C.C

D.D

答案

参考答案：B

解析：

σ已知时，置信区间为故可得答案B。

选择题

某生分析下表，得出了四项结论，其中正确的是（  ）

1957年—1961年全国主要农产品产量（单位：万吨）

A．1957年到1961年我国主要农产品产量在持续下降

B．“ * * ”的“左”倾错误波及到农业生产领域

C．1958年到l960年农产品产量变化的主要原因是“大跃进”和人民公社化运动

D．中央对国民经济实施“八字方针”政策后农村经济迅速恢复和发展
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单项选择题

"Clean your plate!" and "Be a member of the clean-plate club!" Just about every kid in the US has heard this from a parent or grandparent. Often, it’s accompanied by an appeal. "Just think about those starving orphans (孤儿) in Africa!"
Sure, we should be grateful for every bite of food. Unfortunately, many people in the US take a few too many bites. Instead of saying "clean the plate," perhaps we should save some food for tomorrow.
According to news reports, US restaurants are partly to blame for the growing bellies (肚子). A waiter puts a plate of food in front of each customer, with two to four times the amount recommended by the government, according to a USA Today story.
Americans traditionally associate quantity with value and most restaurants try to give them that. They serve large portions to stand apart from competitors and to give the customers value. They prefer to have customers complain about too much food rather than too little.
Barbara Rolls, a nutrition professor at Pennsylvania State University, told USA Today, that restaurant portion sizes began to grow in the 1970s, the same time that the American waistline began to expand.
Health experts have tried to get many restaurants to serve smaller portions. Now, apparently, some customers are calling for this too. A restaurant industry trade magazine reported last month that 57 percent of more than 4 000 people surveyed believed restaurants serve portions that are too large; 23 percent had no opinion; 20 percent disagreed.
But a closer look at the survey indicates that many Americans who can’t afford fine dining still prefer large portions. Seventy percent of those earning at least $150 000 per year prefer smaller portions, but only 45 percent of those earning less than $ 25 000 want smaller.
It’s not that working class Americans don’t want to eat healthy. It’s just that, after long hours at low-paying jobs, getting less on their plate hardly seems like a good deal. They live from paycheck to paycheck, happy to save a little money for next year’s Christmas presents.

According to news reports. US restaurants ______.

A. are partly responsible for the overweight problem
B. ignore the government regulations on food amount
C. serve two to four times the amount the customers want
D. are partly to blame for the waste of food in America
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