问题描述：
英语阅读理解--a factor of 用法的理解
有这么一句：In the United States,for instance ,the mortality rate for lung cancer among female non-smokers has not changed during the past 20 years.During the same period,the rate among female smokers has increased by a factor of half.
a factor of 是女性吸烟比例增长了一半还是增长到了一半呢?
谢谢~!
有这么一句：In the United States,for instance ,the mortality rate for lung cancer among female non-smokers has not changed during the past 20 years.During the same period,the rate among female smokers has increased by a factor of half.
a factor of 是女性吸烟比例增长了一半还是增长到了一半呢?
谢谢~!
问题解答：
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