[单选题]
Under what condition is.g-d 4t *hzgjghi6 /gx+8ot bc(f elk sk9-ik6average velocity equal to the average of the object's initial and fin8+kct- e6skl( bkf9ioal velocity?
A. The acceleration must be constantly changing.
B. The acceleration must be constant.
C. This can only occur if there is no acceleration.
D. This is impossible.