求翻译：面对经济危机，当然会有一些明白人出现，凯恩斯就是其中之一。他认为由消费需求和投资需求构成的有效需求，其大小主要取决于消费倾向、资本边际效率、流动偏好三大基本心理因素以及货币数量。所谓消费倾向是指消费在收入中所占的比例，它决定消费需求。一般来说，随着收入的增加，消费的增加往往赶不上收入的增加，当你月收入3000美元时，每月消费2400美元，也就是花了总收入的80%，当收入达到5000美元时，不一定会用掉4000美元，当收入达到10000美元，你不会用完8000美元，在不知不觉中遵循了收入递增而消费递减这样一种规律，消费需求不足由此而起。是什么意思？

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Facing an economic crisis, of course, there are some sensible people, Cairns is one of them. He believes that the consumer demand and investment demand, the demand for effective size depends primarily on marginal propensity to consume, capital efficiency, flow preference 3 basic psychological factor

Facing economic crisis, of course, be some wise appears, Keynes was one of them. He believed that consists of consumer demand and investment demand effective demand, and its size depends largely on the consumption tendency, marginal efficiency of capital, liquidity preference in three basic psycholo