You will choose one that you feel best exemplifies one of the following ideals: rights, liberty, equality, etc.. Some will deal with one ideal, some will cover several. You are arguing that the one you choose is the best and why that ideal is still important today in society. I want you to do more about liberty because the reference you can use is the The Declaration of Independence.
All applicants go through a series of tests that check their level of English and knowledge of formatting styles. The applicant is also required to present a sample of writing to the Evaluation Department. If you wish to find out more about the procedure, check out the whole process.