清洁活动在一天中的其余时间渐渐减少。

Cleaning activity gradually dies down throughout the rest of the day.

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那么此种个人口腔卫生是什么时候开始的呢？ 人的口腔清洁活动可以追溯至现存的历史记录。

When did all this personal oral hygiene start?

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当地一家报纸报道说，11000位大学生参加了周末义务清洁活动，一些公司也组织员工参与其中。

One local newspaper reported that 11, 000 college students had volunteered for cleanup duty over the weekend. Several companies had organized teams of employees to help.

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