Is it correct to submit a manuscript as a writing sample for graduate admission? I am applying to a master program in cognitive sciences and they ask for two writing samples. I have read that published articles and even manuscripts can be good writing samples, however I have the following questions regarding the ethical and/or legal issues of doing so: 


Should I include all the authors as well as their institutions and
e-mails in the manuscript I send?
Should a writing sample include a brief introduction?
What happens if you are not the ONLY author of the paper you want to
submit? Should you specify your contribution? Does it help that you
are the first author?
Can I send just some paragraphs of the manuscript in order to keep my
sample short? If I do this, should I modify all the references so that they are kept in order according to Vancouver style?
Probably a little paranoid but, could the university use/ distribute any results I report in this unpublished manuscript?
Presumably they want a sample of your writing, not the result of you drafting something, somebody else writing it up, some referee suggesting corrections and your advisor giving it final polish and blessing.