The first one isn't right. The second one is "more correct", but I question whether something identified as a single instance ("the circulation group") can be more "common" than something else. Did you possibly mean "popular" rather than "common"?
New words, one handy idiom, and a 2-minute quiz — delivered to your inbox to keep your streak alive.
AnonymousI joined the circulation group, which was the most common and was divided in two.That one is the better sentence, but I don't understand what you are saying.