U of Pitts 匹兹堡大学 essay

2011匹兹堡大学申请的Personal Essay
题目是这样的：Provide us with a brief statement of about 500 words in which you address one of the following topics:‘Describe an experience that has led you to choose your current career objective’ or ‘Describes a significant experience,achievement,risk you have taken,or ethical dilemma you have faced and its impact on you.’ In your response,be sure to include how the experience will impact your time at the University of Pittsburgh.
Also,if there is anything you did not get a chance to communicate elsewhere in your application,include in a separate paragraph at the end of your essay (ex.,another campus you wish to be considered for,a unique accomplishment or special need).
请问用我的PS可以吗?还是要单独写一篇,然后又在其他地方再单独传PS.
意思就是这是叫我交PS吗,还是叫我交命题作文?
如果是大家对写这篇文章有什么建议?