You breathe it in, it infects the cells of your respiratory tract, and the virus begins to reproduce, and then it spreads throughout your body.

你将之吸入,病原体感染了呼吸道细胞,病毒开始繁殖,接着传遍你的全身

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That virus is reproducing inside cells of your respiratory tract.

病毒在你的呼吸道细胞内繁殖

耶鲁公开课 - 生物医学工程探索课程节选