Recently in the hope of earning both money and social experience, I became a door-trw door salesman. I once read a saying. "If somebody wants something of yours, you will be treated as warmly as spring, but if they don't you may be treated as coldly as winter." You may consider this an exaggeration  , but if you are a salesman, it is clearly correct. You would never have found it to be so true if you hadn't been a salesman. You needn't stand doubtful looks and unfriendly comments; you needn't listen to something completely wrong and nod to say that it was quite right, you needn't worry about being refused time after time; you needn't always keep patience and a smile; you needn't repeat the same sentences over and over again; you needn't talk to somebody you dislike .... I did this work for a month, then I decided to give it up; Apart from the reasons above, I found I was paying too much attention to the job and thus sacrificing my study time. The latest test result proved that my grades were getting worse. Even worse, I hadn't enough time to join my classmates in college activities. Some times 1 felt lonely and unhappy because of both my study and my part-time job. Now I don't think it is worth doing such a thing for even though I was earning money it came at great cost. Newspapers and magazines often publish stories about excellent students who do part-time work while also keeping high scores in class. But according to my experience, park-time work can have some strong negative influences on study. Most students don't view the relationship between study and work correctly. In my opinion, if it isn't a must for financial reasons, students should be careful about taking up a part-time job. From the text, we can tell that the writer is   _  .
an unemployed man a middle-school student a college student a door-to-door salesman