The World Health Organization says it needs to see clear evidence of sustained community transmission of the swine flu virus from person-to-person in at least two regions of the world before it raises its alert to the phase six pandemic level.

VOA: standard.2009.05.14

So, this raises kind of an interesting question in terms of what the difference is between these two cases, and we're talking about numbers of energy.

那么，到这里就出现了一个很有意思的问题,那就是下面这两种情况的区别在哪里？,当然我们关心的是能量的多少。

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