If you lie in bed for eight hours, you may have rested, but you can still feel exhausted the next day.

如果你在床上躺了8个小时，你可能得到了休息，但第二天仍然会感到疲惫。

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He sleeps eight or nine hours a day.

他每天睡八到九个小时。

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Usually, you must sleep for at least seven to eight hours every day, or you will get dark circles under the eyes.

通常，你必须每天至少睡7-8小时，否则你会有黑眼圈。

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