The answer lies in two associated differences among the species, in their digestive systems and body sizes.

答案在于两个相关的物种之间的差异，它们的消化系统和体型。

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Food passes through their digestive systems so quickly, they must eat almost constantly to stay alive.

食物很快地经过它们的消化系统，为了生存它们必须不断的吃东西。

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That helps keep toxic metal out of forests, fields and waterways-and the digestive systems of humans who eat game animals.

这就防止了有毒金属物流入森林、田野和水路等区域，并且在人们在吃猎杀的动物时防止吸收这些有毒物质。

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For example,animal waste and cattle digestive systems release methane gas.

VOA: special.2010.01.05

The respiratory system, for example, the renal system, the digestive system, these are examples - three examples of organ systems that contact the external environment.

例如,呼吸系统,泌尿系统,消化系统,这些系统,这三个系统,与外环境相联系

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And because it's dissolved, it passes more easily across gills and into digestive systems.

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Premature infants, who make up two-thirds of infant deaths, often suffer serious health problems at birth, with undeveloped lungs, organs and digestive systems.

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The larvae of the cheese fly (Piophila casei) are added to the cheese, and the acid from their digestive systems breaks down the cheese's fats, making the final product soft and liquidy.

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