Combined with foreign and domestic research data, we found: Subjects age span is imbalance, there are more research on the elderly and less on young people and children relatively.

综合国内外的研究资料发现：研究对象年龄跨度不平衡，针对老年人的研究比较多，对青少年和儿童的研究比较少。

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People lived shorter lives and so they didn't get far enough into the age span to suffer from the chronic diseases that people are suffering more today.

当时的人寿命比较短所以他们,活不到现代人那么长,长得足以患上那些慢性疾病

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At 55, Mr. Middleton is on the older end of his adventure group's age span.

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Sustained and reinforcing education is needed to effectively encourage people across the age span to take steps to reduce their risk for infection.

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All this activity occurs early in the life span of a galaxy, before it settles down into a quiet middle age.

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