Since 1991 the infant mortality rate and that of children under five years of age have declined at an annual rate of 4.6 percent and 4.9 percent.是什么意思_Since 1991 the infant mortality rate and that of children under five years of age have declined at an annual rate of 4.6 percent and 4.9 percent.在線(xiàn)翻譯_英語(yǔ)_讀音_用法_例句