Block A of mass M is on a horizontal surface of negligible friction. An identical block B is attached to block A by a light string that passes over an ideal pulley. The tension force exerted on block A after the system is released from rest has magnitude T. Block B is then replaced by a block of mass 2M and the system again released from rest.. Which of the following is a correct expression for the tension force now exerted on block A?

A. 12T
B. 23T
C. 34T
D. 43T
E. 2T