A small box of mass m is placed on top of a larger box of mass 2m as shown
in the diagram at right. When a force F is applied to the large box, both boxes accelerate to the right with the same acceleration. If the coefficient of static friction between the lower block and the upper block is μs and the coefficient of kinetic friction between the lower block and the floor is μk, which two of the following statements must be true?

A) The force of friction between the blocks is smaller in magnitude than the force F.
B) The force of friction between the lower block and the floor is equal to 3μkmg.
C) The friction force on the upper block is directed towards the left.
D) The force of static friction acting on the system is greater than the force of kinetic friction acting on the system.