Many people, including health professionals, have assumed that e-cigarettes are safer than traditional cigarettes, because e-cigarettes use heated liquid vapor (蒸汽) rather than burning tobacco leaves in a process that is likely to cause cancer. But “safer” doesn't mean “risk-free”. A troubling increase of acute lung disease among e-cigarette users across 25 states makes us realize that there are still a lot of unknown health implications of smoking e-cigarettes.Last week, the Centers for Disease Control and Prevention (CDC) took the unusual step of warning the public against using any electronic cigarette devices until the agency concludes an investigation into the mysterious outbreak of lung disease. The CDC started a multi-state investigation in mid-August after receiving more than 150 reports of serious respiratory distress (呼吸窘迫) among e-cigarette users, many of them teenagers and young adults. Within a couple of weeks, dozens more cases were reported, including the death of one e-cigarette user in Illinois.Ultimately, it turns out that the outbreak of lung disease is caused by the illegal use of drugs in e-cigarette devices. But even so, such a finding would not mean that users of commercial nicotine (尼古丁) e-cigarettes can breathe easier. There are some pretty unpleasant things floating in that liquid nicotine that may be harmful to our health.3. What caused the outbreak of lung disease among e-cigarette users?A The unpleasant things floating in liquid chemicals.B The commercial liquid nicotine.C The frequent reuse of the same device.D The illegal drugs in e-cigarette devices.

Many people, including health professionals, have assumed that e-cigarettes are safer than traditional cigarettes, because e-cigarettes use heated liquid vapor (蒸汽) rather than burning tobacco leaves in a process that is likely to cause cancer. But “safer” doesn't mean “risk-free”. A troubling increase of acute lung disease among e-cigarette users across 25 states makes us realize that there are still a lot of unknown health implications of smoking e-cigarettes. Last week, the Centers for Disease Control and Prevention (CDC) took the unusual step of warning the public against using any electronic cigarette devices until the agency concludes an investigation into the mysterious outbreak of lung disease. The CDC started a multi-state investigation in mid-August after receiving more than 150 reports of serious respiratory distress (呼吸窘迫) among e-cigarette users, many of them teenagers and young adults. Within a couple of weeks, dozens more cases were reported, including the death of one e-cigarette user in Illinois. Ultimately, it turns out that the outbreak of lung disease is caused by the illegal use of drugs in e-cigarette devices. But even so, such a finding would not mean that users of commercial nicotine (尼古丁) e-cigarettes can breathe easier. There are some pretty unpleasant things floating in that liquid nicotine that may be harmful to our health. 3. What caused the outbreak of lung disease among e-cigarette users? A The unpleasant things floating in liquid chemicals. B The commercial liquid nicotine. C The frequent reuse of the same device. D The illegal drugs in e-cigarette devices.