A block of mass M is pulled along a horizontal frictionless surface by a rope of mass m. If a force P is applied at the free end of the rope, the force exerted by the rope on the block is :

Question

( A ) $\frac{PM}{M+m}$
( B ) $\frac{Pm}{M-m}$
( C ) $\frac{Pm}{M+m}$
( D ) $P$