人均年收入到1000至2000美元时，生育率开始降低，收入到4000至10000时，生育率降到生育等值更换水平（见图表2）。

Fertility starts to drop at an annual income per person of $1, 000-2, 000 and falls until it hits the replacement level at an income per head of $4, 000-10, 000 a year (see chart 2).

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等值债券两种或以上对债券偿付与抵押收入权利相等的债券。

Parity bond Two or more bond issues with equal rights to bond payments and pledged revenues.

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