Well, one reason is that there are developmental disorders that seem to involve damage to one system but not to another.

一个原因是,发展障碍看上去,只会对某一个系统产生损害,而不会损害其他系统

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The reason for that complexity is because your immune system needs to be able to respond to all the potential foreign invaders that we could encounter.

整个系统之所以如此复杂是因为,免疫系统需要应对所有,我们要面对的来犯之敌

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