[名词解释]听觉的辨别阈限

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The recent, apparently successful prediction by mathematical models of an appearance of El Nifio—the warm ocean current that periodically develops along the Pacific coast of South America -- has excited researchers. Jacob Bjerkness pointed out over 20 years ago how winds might create either abnormally warm or abnormally cold water in the eastern equatorial Pacific. Nonetheless, until the development of the models no one could explain why conditions should regularly shift from one to the other, as happens in the periodic oscillations between appearance of the warm El Nifio and the cold so-called anti-El Nifio. The answer, al least if the current model that links the behavior of the ocean to that of the atmosphere is correct, is to be found in the ocean.
It has long been known that during an El Niflo, two conditions exist: (1) unusually warm water extends along the eastern Pacific, principally along the coasts of Ecuador and Peru, and (2) winds b
A. introduction to a new explanation of a physical phenomenon.
B. explanation of the difference between two related physical phenomena.
C. illustration of the limitations of applying mathematics to complicated physical phenomena.
D. indication of the direction that research into a particular physical phenomenon should take.