"I am a professor."
Translation:Ich bin Professor.
It depends on the sentence. In this case, the person is stating their profession. That just happens to be one of the cases where the German sentence drops the indefinite article. Here's a link that explains the profession article dropping: http://german.about.com/od/verbs/a/German-Grammar-TipProfession.htm
What exactly did you put? All possible translations are already accepted. It's either "Ich bin (ein) Professor" (male) or "Ich bin (eine) Professorin" (female). It sounds more natural without the article, but if you don't drop the article, you need to use the correct one.
If this was a multiple-choice challenge, you had to select ALL correct translations. If there's more than one correct translation, it's not enough to select just one.