[单选题]
When is the average veloc d37/hozty5xdk6sl;+vc 4 xbk ityu,ncz j,ew6-q how hr )sus*(.:mm9znzx / g,a of an object equal to the instantaneous velocity?
A. always
B. never
C. only when the velocity is constant
D. only when the velocity is increasing at a constant rate