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
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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
单项选择题
According to the passage, ______ .
A．Cheng Ho succeeded in recaptured the deposed former emperor
B．Cheng Ho once terrorized the islands near Sumatra
C．Cheng Ho hoped to trade with African countries but failed
D．Cheng Ho ruled the entire South Pacific and Indian Ocean
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