I missed four chemistry classes.

我旷了四节化学课。

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I've missed four chemistry classes.

我是旷了四节化学课。

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As a comprehensive course of practice, exploratory study is an enrichment to and expansion of itself in chemistry classes.

研究性学习属于综合实践课程，在化学课堂教学中开展探究学习是对研究性学习内涵的补充和外延的拓展。

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But for their chemistry classes they will benefit from an in-person, high-quality, artisanal curriculum.

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After taking organic chemistry classes at Colorado State University near her home in Fort Collins, Taylor applied to three medical schools.

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The lutetium oxide from which the crystals are made (in only a slightly updated process from the way we all made copper sulphate crystals in high school chemistry classes) all came from China.

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