50.（In the United States, forinstance, the mortality rate for lung cancer among female non-smokers has notchanged during the past 20 years. During the same period the rate among femalesmokers has increased by a factor of half.）In South-East Asia, more than 85 percent oforal cancer cases in women are caused by tobacco habits.
【正确答案】：例如，在美国，在过去的20年中非吸烟女性中肺癌的死亡率并未发生变化。而同期该比率在吸烟女性中增加了一半。
【题目解析】：括号部分包括两个简单句。for instance作为插入语放在句中，翻译时应提到句首；the mortality rate意为“死亡率”；non-smokers是合成词，表示“非吸烟者”。the rate指上文提到的the mortality rate；increase这个词后面通常跟by引导的介词短语，表示增幅；by a factor of后面跟倍数或比率，表示具体增幅情况。
