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问题 单项选择题

假定在某一产量水平上，某一厂商的平均成本达到了最小值，这意味（）

A.边际成本等于平均成本

B.厂商获得了最大利润

C.厂商获得了最小利润

D.厂商的经济利润为零

答案

参考答案：D

判断题

身体分节对促进动物体的新陈代谢，增强对环境的适应能力，有着重大意义。环节动物开始有同律节现象。（）
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单项选择题

Many researchers believe that the presence of RNA in brain cells is the biochemical basis of memory; that is, the presence of RNA enables us to remember. Because certain chemicals are known to inhibit the synthesis of RNA in the body, we can test this hypothesis. Animals that have learned particular responses can be injected with an RNA inhibitor and then tested for memory of the learned responses. Which of the following test results would most seriously weaken the case for RNA as the basis of memory

A．After an injection of RNA inhibitor, a wide range of behaviors in addition to the learned responses were affected.

B．After an injection of RNA inhibitor, animals that had not consistently been giving the learned responses were able to give them consistently.

C．After injections of RNA inhibitor, some animals lost memory of the learned responses totally but others lost it only partially.

D．After a small injection of RNA inhibitor, animals responded well, but as the size of the injection increased, they gave fewer of the learned responses.

E．(E) After an injection of RNA inhibitor, animals could not learn a new response.
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