If U and O are the only students serving on commission B, how many of the nine student must serve on commission C?

Nine students—O, P, Q, R, S, T, U, V, and W—are the only student who can serve on three commissions designated A, B, and C, and each student must serve on exactly one of the commissions. Commission A must have exactly one more member than does commissionB. It is    
possible that there are no members of commission C Neither O nor P nor Q can serve on commission A. Neither R nor S nor T can serve on commission B. Neither U nor V nor W can serve on commission C.