Block A of mass m is placed on block B of mass M lying on a smooth horizontal surface. A horizontal force F is applied to B such that A does not slide over B. Which statement correctly gives the directions of the frictional forces acting on A and on B at their common surface?
a) On A: opposite to F ; on B: towards F
b) On A: towards F ; on B: opposite to F
c) On A: towards F ; on B: towards F
d) No friction acts on either block