Blocks A (2kg) and B (3kg) are in contact on a smooth horizontal surface. A horizontal force of 10N is applied to block A, pushing both blocks to the right. What is the magnitude and direction of the force exerted by block B on block A?
a) 10N, to the left
b) 4N, to the left
c) 6N, to the left
d) 6N, to the right