since it is a circular perm, teachers can be arranged in (4-1)! Once this is done, students can be arranged 4! ways in between.
total arrangements = (4-1)! * 4!
Thanks, Dan. Initially, I thought teachers and students can be regarded as 1 person in the following pattern: TS TS TS TS. Then, permutation would be 3!*2*2*2*2. What's wrong with this approach?
By the way, the OA is D.