There are usually several different strains of influenza active at any time, and these variations evolve.

一般在同一时候都有好多种不同的流感病毒株在活跃，而且这些病毒株在不断变异。

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There are usually several different strains of influenza active at any time, and these variations evolve.

一般在同一时候都有好多种不同的流感病毒株在活跃，而且这些病毒株在不断变异。

youdao