• 2022-06-08
    Which
    one of the following is the reason of pandemic
    flu
    ()
    A: virus
    has strong virulence
    (B)HA
    of Influenza
    B: virus
    easily produce variation, and people lack of immunity
    (C)
    NA of Influenza
    C: virus
    easily produces variation, and people lack of immunity
    (D)
    Influenza
    D: virus
    develops new subtype virus, and people lack of immunity