For four particles A, B, C & D, the velocities of one with respect to other are given as V DC is 20 m/s towards north, V EC is 20 m/s towards east and V BA İS 20 m/s towards south. Then V DA IS:
A. 20 m/s towards north
B. 20 m/s towards east
C. 20 m/s towards south
D. 20 m/s towards west.