问题 单项选择题

在完全竞争市场上,厂商得到的价格若低于以下哪种成本就停止营业( )

A.平均成本

B.平均可变成本

C.边际成本

D.平均固定成本

答案

参考答案:B

解析:[分析]
如图7-1所示,当厂商面对的需求曲线低于平均成本曲线的最低点时,相对于任何产量水平的短期平均成本都高于价格即平均收益,这意味着厂商在选择任何产量水平时都会蒙受损失。在这种情况下,厂商究竟是亏损经营,还是停止营业,这要取决于产品价格能否抵偿其平均可变成本。如果需求水平高于AVC曲线的最低点,厂商应继续营业;如果需求水平低于AVC曲线的最低点,厂商应停止营业。这是因为厂商在短期内无论是否生产,都必须为固定投入支付固定成本,如果它停止营业,则它要损失全部固定成本。所以,只要存在着使P>AVC的产量,厂商就应该继续生产,并根据MC=MR的原则确定产量(Q0),这样其平均收益就不仅能补偿平均可变成本,而且还能补偿部分平均固定成本,从而使亏损减少到最低限度。如果不存在使P>AVC的产量,则意味着厂商在任何产量水平上的平均收益都不仅不能补偿任何数量的平均固定成本,而且不足以补偿平均可变成本。在这种情况下,厂商应停止营业以使亏损减少到最低限度,因为这样至少可以避免可变成本的部分损失。因此,本题应选择B项。
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阅读理解

阅读理解.

      When one person gains weight , their close friends oftenfollow. Researchers have just

offered evidence in a study that says obesity (肥胖) appears to spread through social ties.

But the findings might also offer hope.

      If friends help make obesity acceptable , then they might also be influential in losing the

fat.The researchers note that support groups are already an effective tool in dealing with

other socially influenced problems , likealcoholism (酗酒 ) .

     The findings appeared in the New EngLand Journal of Medicine. The researchers used

information collected from 12, 000 people. It was collected between 1972 and 2003 as

part of the Framingham Heart Study.

     The information was highly detailed. There was even contact information(联络信息 )

for close friends of the people in the study.

     The researchers examined more than 40 , 000 social ties. They found a person's

chances of becoming severely overweight increased by 50% if a friend had become

obese.

     A sister or brother of a person who became obese had a 40% increased chance of

becoming obese. The risk for a wife or husband was a little less than that.

     Nicholas Christakis of Harvard Medical School was a lead researcher in the study.

He says there is a direct causal relationship (因果关系) betweena persongetting fatand

being followed in weight gain by a friend.

     The study found that the sex of the friends was also an influence. In same-sex

friendship, a person had a 71%increased risk of becoming obese. Men had a 44%

increased risk of becoming obese after weight gainin a brother. In sisters ,it was 67% .

     The researchers also considered the effect of where people lived in relation to each

other. James Fowler of the University of California,was the other lead expert. He says

a friend who lives a few hundred kilometers away has as much influence as one in the

same neighhorhood. He says the study demonstrates the need to consider that a major

part of people's health is tied to their social connections.

     Both researchers say their research shows that obesity is not just a private medical

issue , but a public health problem.

1. What does the underlined sentence in Paragraph 2 mean?______

A. Obesity is a negative influence on close friends.

B. Friends might also play a part in losing weight.

C. One might have positive influence on one's friend.

D. Friendship may have little to do with one's health.

2. Which of the following statements would Nicholas Christakis agree to?______

A. If one gains weight, one's friends are likely to get fat.

B. Social problems like alcoholism are easy to deal with.

C. Friends usually don't follow each other to lose weight.

D. One might influence others on their social behavior.

3. The increased risk of gaining weight by an obese sister is _______.

A. 50%

B. 40%

C. 67%

D. 71%

4. James Fowler seems to believe that________.

A. a friend who lives nearby affects us most

B. one's health has nothing to do with friends

C. social connections have effects on one's life

D. a friend living faraway has the same influence as one's neighbor

5. The author makes his point clear in the text________.

A. a major part of people's health is based on their genes

B. friends living closer have greater influence on one's health

C. social relationship is closely connected with people's health

D. people's physical condition is subject to social connections

单项选择题