They fast on certain days.

他们在某些天斋戒。

《新英汉大辞典》

All religions have certain days when people refrain from eating and excessive eating is one of Christianity's seven deadly sins.

在所有宗教中，人们都在某些特定的日子不吃东西，过量饮食是基督教的七宗大罪之一。

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Regular airlines may offer special rates if you book your flights in advance and fly on certain days of the week when they don't expect to have full planes.

如果你提前订好机票，并且在一周中预计不会满员的特定日子乘机出行，通常情况下，航空公司都会提供特价。

youdao

I've certainly worked a lot more than that on certain days.

有些日子工作时间比那个长多了。

电脑图片的魅力 - SpeakingMax英语口语达人

Now the story of creation in Genesis 1 takes place over seven days, and there's a certain logic and parallelism to the six days of creating.

创世纪》第一章中的创世在七天内完成，它和六天创世的故事在逻辑上有一些对照。

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Then there are certain holy days: and they are separated and demarcated from common time by special rules that mark them as different.

然后是一些神圣日：,和普通的时间,被一些特殊的判定它们不同的规则所区分开。

耶鲁公开课 - 旧约导论课程节选

You could offer to show up at the store and sell your product on certain days.

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You know, there are certain days that remind me of why I ran for this office.

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Still, there are certain days that have been set aside for all of us to do so.

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