Ok, let's look at the old exams. What can we learn?
Some students just study group theory and hope to pass on that. This is, in theory, possible: Absolutely perfect scores on four problems on group theory would, in some years, be enough to pass the exam. But that's very, very unlikely. First, enough group theory problems are trickly enough that it will be very hard to get perfect scores. Second, 66% isn't guaranteed to pass, and even if it does, it would probably only be a C (especially since graders would look askance at a paper that only answered group theory questions).
Bottom line: You should learn some ring theory and linear algebra too.