但是，如果你有一段时间没有锻炼过了，并且有健康方面的问题，那么在你开始一项新的健身计划之前，可能想先和医生讨论一下。

But if you haven't exercised for some time and you have health concerns, you may want to talk to your doctor before starting a new fitness routine.

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And we haven't talked about reactions at all yet, so you don't need to worry about the specifics of that exactly, but just that if you have this negative change in energy, you have a more stable product than you do reactant.

当然我们还没有开始讨论反应，所以你不用担心它的细节是怎么样的，你只需要知道，如果能量的变化是负值，那么你将得到一个比反应物更稳定的生成物。

麻省理工公开课 - 化学原理课程节选