单项选择题

According to the passage a great variety of influenza can appear when ______ .

A．H and N spikes are produced
B．animal and bird viruses are combined
C．dissimilar types of viruses recombine
D．two viruses of the same type are contracted

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热门试题

单项选择题

New strains of viruses are transmitted to man by ______ .

A．A type of wild pig
B．diseased lower animals
C．a group of migrating birds
D．a variety of means

单项选择题

It can be inferred from the passage that all of the following are with of producing new strains of influenza viruses except ______ .

A．two influenza viruses in the same animal recombining
B．animal viruses recombining with human viruses
C．two animal viruses recombining in one animal
D．two animal viruses recombining in a human