The formula that describes an object's motion is given by s=ut+1/2at^2, where s is the distance traveled, u is the initial velocity, a is the acceleration, and t is the time. Which equation represents a in terms of the other variables?

A. a=2s-2u/t

B. a=2s+2u/t

C. a=2s-2ut/t^2

D. a=2s+2ut/t^2