That is, most processes that we're concerned with, they'll happen with something held constant like pressure or temperature or maybe volume.

这句话是说我们所关注的大部分过程，发生的时候都是保持某个量为常数,比如压强，温度或者体积。

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And he kept track of how many people he gave the vaccines to, and then he kept track of what would happen to those people when a smallpox infection occurred in their community.

他与接种过牛痘的人保持联系,关注当天花在这些人周围肆虐时,他们身上发生了什么

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