单项选择题

It has been discovered that ______.

A．H5N1 does not transmit among human beings
B．bird flu spreads only among birds
C．H5N1 is a variant of flu virus
D．bird flu adapts easily to other species

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热门试题

单项选择题

H5N1 is a flu strain ______.

A．limited to Hong Kong
B．which first affected human beings in 1961
C．crossing species barriers
D．which was first isolated from American birds

单项选择题

The Spanish flu was the worst plague in history because ______.

A．it led to a terrible loss of human life
B．it was the earliest kind of flu
C．it broke out after World War One
D．it infected many animals as well