They change sugar into acids, which break down the tooth's harder outer covering.

它们把糖转化成酸，酸会腐蚀较硬的牙齿外层。

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The cells of an animal have a bag-like outer covering, called a membrane.

动物细胞有一个口袋状的外层，叫细胞膜。

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The outer covering of the egg is waterproofed to prevent the embryo from drying out.

鸡蛋的外壳是不透水的，防止胚胎失水。

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Approximately 30 percent of the cottonseed's weight is in the hull, or outer covering.

NPR: Texas Cotton: 'Farmer Profits at Every Step'

The husk, the outer covering of the barley grain, is placed in a bi-fermentor which transforms the cellulose into methane gas.

CNN: Brewing giant Carlsberg's sustainability drive pays off

The outer covering was a windproof and water resistant shell.

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