自1970年以来，美国吸烟人口的比重大幅下降，从近40%下降到了20%左右。但是，这一比重大约从2004年起就不再下降。

The share of Americans who smoke has fallen dramatically since 1970, from nearly 40 percent to about 20 percent, but the rate has stalled since about 2004.

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脊灰病例自1988年以来减少了99%以上，从当时逾125个流行国家中估计的35万病例，下降至2010年的1349起报告病例。

Polio cases have decreased by over 99% since 1988, from an estimated 350 000 cases in more than 125 endemic countries then, to 1349 reported cases in 2010.

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脊灰病例自1988年以来减少了99%以上，从当时逾125个流行国家中估计的35万病例，下降至2009年的1604起报告病例。

Polio cases have decreased by over 99% since 1988, from an estimated 350 000 cases in more than 125 endemic countries then, to 1604 reported cases in 2009.

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