A man weighing 80 kg is standing in a trolley weighing 320 kg. The trolley is resting on frictionless horizontal rails. If the man starts walking on trolley with a speed of 1m/s, then after 4 seconds his displacement relative to the ground will be
A. 5 m
B. 4.8 m
C. 3.2 m
D. 3.0 m