Because you see, also motivation and energy-- you don't need research for that, you know that when you are feeling good, you have more motivation, you have more energy-- of course, there is a lot of research to back that up.

因为动力和精力-,不需要研究就能明白，你知道感觉好时，动力和精力更充沛-,当然有很多研究支持这一点。

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