Answer questions below.

1.

A block is set on a table, where there is negligible friction between the block and the table. The block is connected to an identical hanging block by a lightweight string that passes over an ideal pulley as shown. When the blocks are released from rest, the two-block system gains kinetic energy because work is done on the system. Which type of force or forces make a nonzero contribution to the net work done on the two-block system? (A) Gravitational force only B Gravitational force and tension only Gravitational force and normal force only D Gravitational force, tension, and normal force