Posted on the right is the list of already chosen articles. If you did not sign before the break you can use this list as a guideline of what is taken. However, it will be first come, first serve after the break - if you work on one (during the break), and someone else is working on the same one, and neither of you signed the list before you left - the first person to sign the sheet after the break gets it, the other person will be out of luck.
Sounds harsh, but you had one full class, and over a week's time to find an article and sign up for it.