Well, when Pavlov, for instance, started before conditioning there was simply an unconditioned stimulus, the food in the mouth, and an unconditioned response, saliva.

比如，在条件作用形成之前,只是简单的存在着无条件刺激，即食物，以及无条件反应，即唾液。

耶鲁公开课 - 心理学导论课程节选

But again, the elements were harsh, finding food may not have been easy, and certain sorts of diets would prevail over others, where there would be a lot of certain nutrients and few of other ones.

可是,自然环境是恶劣的,寻找食物一点也不简单,不过某些食物相对其他更为常见些,其富含有某些营养成分,但缺乏其他的

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