令人惊讶的是，钙的补充品中可能受到铅的污染，因为主要的钙补充品像海贝和牛骨都可能被污染。
Surprisingly, calcium supplements may be contaminated with lead, because the sources of calcium in supplements—like seashells or cow bones—are contaminated.
同时，水泥中的钙离子也会吸收水分和二氧化碳，形成碳酸钙——碳酸钙是贝壳的主要成分。
Meanwhile, calcium ions in the cement also absorb moisture and carbon dioxide, forming calcium carbonate -- the material found in seashells.
例如萤火虫，它主要是依赖于镁离子这种辅助因子，而水母则依赖于钙离子。
Like fireflies, they too rely on a cofactor, in this case calcium ions rather than magnesium.
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