Viruses change,or mutate, so flu vaccines must be reformulated each year to target the most common threats.

VOA: special.2009.03.04

In 1957, they reformulated it and they called it the Standard & Poor 500, but I'm using their long theories, back to 1871, so I can't call it the 500; I'm calling it the Composite.

在1957年,他们将其重建,并命名为标准普尔500指数,但这里用到的是1871年发布的理论,所以不能称之为500,我称之为综合指数

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