Two blocks with masses M and m are in contact with each other and are resting on 2 horizontal friction less floor. When horizontal force F is applied to the heavier, the blocks accelerate to the right. The force between the two blocks are

A

$$\frac{mF}{M + m}$$

B

$$\frac{MF}{m}$$

C

$$\frac{mF}{M}$$

D

$$\frac{(M + m) F}{m}$$