紫外线和氯先后作用的消毒效果优于紫外线和氯同时消毒。

However, different combination modes and different doses of UV and chlorine affect the inactivation effect.

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方法收集33例先后作CT和TVS检查的女性盆腔肿块病例，均经手术和病理证实。

Methods 33 eases of female pelvic masses confirmed by operation and pathology were retrospectively studied with CT and TVS.

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先后作为哈佛经济系的返回本科生和博士生，我上过他的高级经济理论和经济思想史的课程。

First as a returning undergraduate and then as a doctoral student in economics at Harvard, I attended his courses on advanced economic theory and the history of economic thought.

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