Two blocks, C (1.5kg) and D (2.5kg), are in contact on a frictionless horizontal surface. A constant horizontal force of 12N pushes block C toward block D, and the blocks accelerate together. Which of the following is closest to the magnitude of the force that block D exerts on block C?
a) 4.5N
b) 8.0N
c) 6.0N
d) 12N