"With the first subject, after about 20 hours of training, his digit span had risen from 7 to 20," Ericsson recalls.

“对于第一个实验对象，经过大约20小时的训练，他的数字跨度从7上升到20。”爱立信回忆道。

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But he points out that most roofs, whether tile or asphalt-shingle, have a life span of 20 to 25 years.

但他指出，无论是屋瓦还是基于沥青材料的盖屋板，多数的屋顶的生命周期都约为20 - 25年。

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I wondered if 50 years had just simply flashed by or whether that boy and I had just simply changed places in the span of 20 seconds.

我有点迷惑，50年是否就已这么转瞬即逝，还是只不过我和那个男孩在20秒的时间里互换了位置。

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