A person travels along a straight road for the first half length with a velocity `v_(1) ` and the second half length with velocity ` v_(2)`. What is the mean velocity of the person ?
A. `v_(1)v_(2)`
B. `(v_(2)^(2))/(v_(1)^(2))`
C. `(v_(1)+v_(2))/(2)`
D. `(2v_(1)v_(2))/(v_(1)+v_(2))`
