So most mollusk shells have an interior layer of aragonite to maintain their internal pH level.

因此，大多数软体动物的外壳都有一层文石内层，以维持其内部 pH 值。

We even have buffers in our blood to keep our internal pH constant and ourselves healthy.

我们甚至在我们的血液中有缓冲剂来保持我们内部的 pH 值恒定和我们自己的健康。