Study Design. Prospective, observational study.

研究设计：前瞻性观察研究。

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The smoking situation is taken from an observational study in early 2008.

图中所示吸烟情况源自2008年初一项观察性研究。

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The smoking situation is taken from an observational study in early 2008.

图中所示吸烟情况源自2008年初一项观察性研究。

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