Which are root words? Check all that apply

Root words are parts of words which cannot be divided any further, but which have some kind of meaning on their own. Here, I believe that root words are cred, graph, and vis.

Cred (as found in credible, credibility), means something believable; graph (as in graphic) means to write; vis (as in visible) means to see. Anti, con, and post are all prefixes, which means they are added to words and cannot be root words thus.