The last three years have been (years for belonging as AOS):
2011: "Compose a creative piece..."
2010: "Select one of the following quotations for a piece of imaginative writing..."
2009: "Drawing on the ideas in ONE of these quotations, construct an imaginative piece..."
So you can see all the last three years invites you to write some form of fictional text, the medium of your own choosing.
However, apparently there has been a new head of English at BOS, so this trend may not continue. But I doubt the new head would change the format much, seeing as she's new. But I'm purely speculating now.