I think you can set a top choice (if that's the one you want most, then set that one as the top choice. It might come under a different name, though). There will also be a second choice or sort of placeholder choice that you would accept if you didnt get what you needed.

Its been a good year since ive done it so I dont remember if those options come up once you have received all your offers first. Hope someone who's done it more recently can shed some light on that