Two Blocks,B1 and B2 with Masses of 12

Multiple Choice

Two blocks,B1 and B2 with masses of 12.0 kg and 5.60 kg,respectively,are in contact with each other on a frictionless horizontal surface.A purely horizontal force of 30.0 N is applied to B1,which in turn pushes B2 and both blocks accelerate together uniformly.The net horizontal force acting on B2 is

A) 9.55 N.
B) 15.0 N.
C) 20.5 N.
D) 30.0 N.
E) 60.0 N.