Liúgǎn bìngdú zhǔyào qīnsī hūxīdào.
The influenza virus primarily attacks the respiratory tract.
Yānwù duì hūxīdào yǒu hěn dà shānghài.
Smoke causes great harm to the respiratory tract.
Yīshēng shuō tā yǒu hūxīdào gǎnrǎn.
The doctor said he has a respiratory tract infection.
