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).
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.
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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