If a particle travels a linear distance at speed `v_(1)` and comes back along the same track at speed `v_(2)`.
A. its average speed is arithemtic mean `(v_(1) + v_(2))//2`
B. its avcrage speed is geometric mean `sqrt(v_(1) v_(2))`
C. its average speed is harmonic mean `2v_(1)v_(2)//(v_(1) + v_(2))`
D. its velocity is zero
