A weird thing which is discussed in the textbook is if you wait a while and then you try it again with the bell after a couple of hours, the saliva comes back.
教材中讨论了一件奇怪的事情，如果你稍等一会，在几个小时之后用铃声重新去尝试，狗会重新开始分泌唾液。
Then, when it seems we will never smile again, life comes back.
然而，当我们似乎永远不会再微笑的时候，生活又回来了。
We put turbines in the mouth of a river. Then, when the tide comes up, it turns the turbines, and when it runs back towards the sea, it turns them again.
把水轮机放在河口，然后当潮水上涨的时候，它能驱动水轮机，而退潮时，又能驱动水轮机。
We put turbines in the mouth of a river. Then, when the tide comes up, it turns the turbines, and when it runs back towards the sea, it turns them again.
把水轮机放在河口，然后当潮水上涨的时候，它能驱动水轮机，而退潮时，又能驱动水轮机。
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