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Do they only belong and serve for certain people in certain time?
它们是否只存在于某些特定时间，服务于特定人群？
youdao
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The classroom teaching is conducted in certain time and limited space.
课堂教学是在一定的时间和有限的空间中开展的。
youdao
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The classroom teaching is conducted in certain time and limited space.
课堂教学是在一定的时间和有限的空间中开展的。
youdao