My father used to be a heavy somker.He smoked more than 20 cigarets each day;therefore,he was the polluter wherever he went.My mother and I tried to persuade him to give it up.He gave it up many times but each time only for a few days or only for a few hours.
       Once he declared that he would stop smoking right away under the pressure of my mother,and he threw his cigarets into the dustbin.The effect of his declaration lasted only for two days.Then I found him smoking again when he thought that he was alone and no one saw him.On the fifth day of his declaration,he smoked openly.
       Last winter he got pneumonia.When he was well again,the doctor ordered him to give up smoking.To our delight,this time he really got rid of the habit.It seems that the doctor's order is more effective than mother's scolding,my suggestion and his own declaration.