In general, chargeable toilets are rather clean. So during the travel time, it's necessary for you to bring some change.

一般来说，有人收费的厕所应该是很干净的，所以旅行的时候有必要带一些零钱，有些地方甚至都会收取手纸的费用。

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But physicists know that time travel is more than just a compelling plot device - it's a serious prediction of Einstein's general relativity equations.

但是，物理学家知道，时间旅行不只是令人信服的秘密装置，而是爱因斯坦广义相对论方程的严肃预言。

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