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问题 单项选择题

导致可口可乐需求曲线向左下方移动的是( )。

A．可口可乐价格的上升

B．百事可乐价格的下降

C．消费者可支配收入的上升

D．年轻人对碳酸饮料偏好的增加

答案

参考答案：B

解析： A项不正确，因为可口可乐价格的上升只会带来需求数量的变化，需求曲线并不会变动；C项和D项不正确，因为消费者可支配收入的上升和年轻人对碳酸饮料偏好的增加会导致需求曲线向右移动。

问答题 简答题

试述离心泵的汽蚀现象？
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单项选择题

The similarity between ichthyosaurs and fish is an example of convergence, a process by which different classes of organisms adapt to the same environment by independently developing one or more similar external body features. Ichthyosaurs were marine reptiles and thus do not belong to the same class of organisms as fish. However, ichthyosaurs adapted to their marine environment by converging on external body features similar to those of fish. Most strikingly ichthyosaurs, like fish, had fins.
If the statements above are true, which one of the following is an inference that can be properly drawn on the basis of them

A．The members of a single class of organisms that inhabit the same environment must be identical in all their external body features.

B．The members of a singly class of organisms must exhibit one or more similar external body features that differentiate that class from all other classes of organisms.

C．It is only as a result of adaptation to similar environments that one class of organisms develops external body features similar to those of another class of organisms.

D．An organism does not necessarily belong to a class simply because the organism has one or more external body features similar to those of members of that class.

E．(E) Whenever two classes of organisms share the same environment, members of one class will differ from members of the other class in several external body features.
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