A body travelling with uniform acceleration crosses two point `A` and `B` with velocities `20 m s^-1` and `30 m s^-1` respectively. The speed of the body at the mid-point of `A` and `B` is.
A. `24 ms^(-1)`
B. `25 ms^(-1)`
C. `25.5 ms^(-1)`
D. `10sqrt(6) ms^(-1)`