Last year the World Health Organization (WHO) warned against using electronic cigarettes, saying there was no evidence to prove they were safe or helped smokers break the habit.

世界卫生组织(WHO)曾在去年提醒人们不要吸电子香烟，称没有证据证明其安全性，以及帮助戒烟的功用。

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Manufacturers claim that electronic cigarettes are a safe alternative to conventional cigarettes.

制造商声称电子香烟是一种安全的香烟替代品。

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"As a result, some people believe that e-cigarettes are a safe substitute for conventional cigarettes," said Prue Talbot, the director of UC Riverside's Stem Cell Center, whose lab led the research.

加利佛尼亚大学干细胞研究中心主管，他的实验室正在进行此项研究。他说：“正因为如此，许多人认为电子烟是安全的，完全可以替代传统香烟。”

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After all, how can you prove that cigarettes are safe and effective?

CNN: Kids, not adults, the focus for cutting tobacco use