A、Whether second hand smoking is liked with cancer. B、Whether active smoking is linked with cancer. C、Whether passive smoking by

Smoking is even more dangerous than previously believed, according to a major review of medical data by the World Health Organization’s cancer agency. The International Agency for Research on Cancer (IARC) also published the first evidence to link second hand smoke with increased risk of cancer.
    The agency convened 29 scientists from 12 countries to review all significant published research on both active and passive smoking. They state explicitly that even an average degree of passive exposure to tobacco products can cause lung cancer in people who have never smoked. "It’s been suspected for a long time," said Professor Richard Doll, one of the report’s authors, "but this is the first time we’ve had a clear scientific consensus saying it’s definitely a cause." Fifty years ago, Professor Doll was a joint author of the first published paper to suggest a link between tobacco and lung cancer.
    The agency’s report also implicates tobacco in five cancer sites not previously shown to be associated with smoking —the stomach, liver, uterine cervix, kidney (renal cell carcinoma), and myeloid leukaemia. "The additional risk to these sites from smoking varies from about 30% to double," said Professor Doll. "Some were previously suspected, but this is the first time there is solid evidence."
    Cancers normally linked to hormonal causes seem to be unaffected by smoking. In particular, the agency’s working group rejected suggestions that passive smoking can cause breast cancer. The agency was unable to provide a definitive answer, however, to the question of whether passive smoke by children in the home is linked to childhood cancers.