GDP is the value of all final goods and services produced within a country's border in a specific period of time, usually a year.

GDP是指一国在某一特定时期(通常为一年)内生产所有商品和服务的最终价值。

Those gas bubbles can puff up bread dough or cake batter, but the acidity of the sour milk isn't all that consistent, so neither were these reactions or their final baked goods.

这些气泡可以使面包面团或蛋糕面糊膨胀，但酸奶的酸度并不是那么一致， 因此这些反应或它们最终的烘焙食品也不是。