The same study found another age effect: Given the same amount of time in bed, older people take longer to fall asleep.

同样的研究发现另一个年龄影响：同样的睡眠时间，老人往往要花费更多的时间才能睡着。

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The age effect is seen because influenza a viruses - the kind considered most likely to cause pandemics - have evolved into two major branches known as type 1 and type 2 flus.

年龄效应可见于甲型流感病毒中。这是一种最可能广泛传播的流感病毒，已经演变出甲1型流感病毒、甲2型流感病毒两个主要分支。

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Thee age effect is seen because influenza a viruses - the kind considered most likely to cause pandemics - have evolved into two major branches known as type 1 and type 2 flus.

年龄效应可见于甲型流感病毒中。这是一种最可能广泛传播的流感病毒，已经演变出甲1型流感病毒、甲2型流感病毒两个主要分支。

youdao

Thee age effect is seen because influenza a viruses - the kind considered most likely to cause pandemics - have evolved into two major branches known as type 1 and type 2 flus.

年龄效应可见于甲型流感病毒中。这是一种最可能广泛传播的流感病毒，已经演变出甲1型流感病毒、甲2型流感病毒两个主要分支。

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