完形填空：阅读下面短文，从短文后各题所给的四个选项（A、B、C和D）中选出可以填入空白处的最佳选项。
John entered a college and often worked late until 12 at night. He fell into the 1 of smoking a year ago. He smoked so much that he 2 had a cigarette on his lips. He 3 while he read, while he watched television and 4 while he drank a cup of coffee or tea. He smoked nearly forty cigarettes a day, but he was 5 about it.
John's friend, Frank, 6 many times to 7 him not to smoke. “Smoking is bad for your 8!” he said, “You'd better give it up. ” But his advice didn't 9.
Before long, John 10 that he often got a bad cough, 11 he went to see a doctor. The doctor 12 him carefully and asked whether he often smoked. John told him the 13. Then the doctor told him that his cough was 14 by smoking and he wouldn't get any better unless he stopped smoking.
“If not,” said the doctor, “you will never 15 from your cough and some other illnesses may also be caused.” John became 16 and made up his mind to give up smoking. At the beginning, it was very 17 for him. Every 18 when he wanted to smoke, he got something to eat. At last, he was not 19 smoking at all. And he no longer had 20.
