人类的这种正常反应是用来保护自身的，这种反应向我们发出危险信号，让我们做好应对危险的准备。

This normal human reaction is used to protect us by signaling danger and preparing us to deal with it.

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当一切准备就绪，信号发出，它们开始鸣叫。

When all was ready a signal was given, and they began their music.

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因此，所有的乘客都仰靠到椅子背上，准备等候司机发信号。

So all the passengers leaned back against seats and got ready for the driver's signal.

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It predicts that the best timing is when the conditioned stimulus, which is the signal, comes before the unconditioned stimulus, which is what you have to prepare for.

它预测，最佳的时机,莫过于作为信号的条件刺激，出现在需要你做准备的，非条件刺激之前。

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