ABC News anchor   Peter Jennings died on Aug.7, 2005 at home in New York after a brief battle with lung cancer. ABC News anchors said they hope if anything good can be taken from Jennings' death, it is a great awareness of the dangers of smoking. "I want to give a message," Barbara Walters said. "If you have kids who are smoking, tell them that we lost Peter." Lung cancer is the worst killer in America, taking more lives each year than any other cancer, according to the America Cancer Society. About 160,440 Americans die each year of cancer, making up 28 percent of all cancer deaths. More than 87 percent of lung cancers are smoking related. Dr. Derek Raghavan, director of the Cleveland Clinic' s Taussing Cancer Center , said that once a person stops smoking, he starts getting better. Three to five years after quitting, the possibility of getting lung cancer is reduced by half. Warning signs of lung cancer can also be mixed with symptoms connected with long-term smoking. The three main warning signs are an increase of coughing that doesn't clear up, coughing up blood and sharp chest pains. People with those symptoms should see a doctor. Raghavan said there have been promising developments in the treatment of lung cancer, including uses of radiation and surgery and drugs. "But the fact is that stopping smoking is the most important thing we can do," Raghavan said. "There is no treatment that even comes close." Anchor Peter Jennings died of lung cancer which was possibly caused by        _  .
his bad eating habit overmuch work long-term smoking the old age
Question: ABC News anchor   Peter Jennings died on Aug.7, 2005 at home in New York after a brief battle with lung cancer. ABC News anchors said they hope if anything good can be taken from Jennings' death, it is a great awareness of the dangers of smoking. "I want to give a message," Barbara Walters said. "If you have kids who are smoking, tell them that we lost Peter." Lung cancer is the worst killer in America, taking more lives each year than any other cancer, according to the America Cancer Society. About 160,440 Americans die each year of cancer, making up 28 percent of all cancer deaths. More than 87 percent of lung cancers are smoking related. Dr. Derek Raghavan, director of the Cleveland Clinic' s Taussing Cancer Center , said that once a person stops smoking, he starts getting better. Three to five years after quitting, the possibility of getting lung cancer is reduced by half. Warning signs of lung cancer can also be mixed with symptoms connected with long-term smoking. The three main warning signs are an increase of coughing that doesn't clear up, coughing up blood and sharp chest pains. People with those symptoms should see a doctor. Raghavan said there have been promising developments in the treatment of lung cancer, including uses of radiation and surgery and drugs. "But the fact is that stopping smoking is the most important thing we can do," Raghavan said. "There is no treatment that even comes close." Anchor Peter Jennings died of lung cancer which was possibly caused by        _  .
A. his bad eating habit
B. overmuch work
C. long-term smoking
D. the old age
Answer: