David and Allan work in the same office．As their father often smokes(吸烟), they both like smoking very much．Sometimes they smoke in the office．Their two workmates(同事) are unhappy because it makes them uncomfortable．They ask them to give up(放弃) smoking, but they can't．One morning Allan coughed(咳嗽) for a long time and his face(脸) turned red．He looked sad the whole morning．

“Smoking is bad for your health, Allan, ”One of his workmates said．“You'd better give it up．”

“You're right, madam, ”Said Allan, “but it's difficult for me to do that．I tried to stop smoking a few times(次), but I failed(失败)．”

“I don't think so．”said David．“it's easy for me．”

“Have you stopped smoking?” asked the woman．

“No,” answered David．“but I can give up smoking twenty times a day!”

根据短文内容，完成下面的句子。

1．David is Allan's           ．

2．There are                people in the office．

3．Their workmates ask David and Allan to give up smoking because                ．

4．Allan looked sad the whole morning because                     ．

5．David said he could               a day．