替换率——用来协调静止人口的总出生率级别。
Replacement rate — The level of total fertility that is compatible with a stationary population.
疾病控制和预防中心最近发布的资料表明近三年来早产的比例连续在下降并在2009年下降到占总出生率的12.18%。
The Centers for Disease Control and Prevention released data recently showing that in 2009 the preterm birth rate declined, for the third year in a row, to 12.18 percent of all births.
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