At time t, the position of a body moving along the s-axis is s=to - 15t + 72t m. Find the body's acceleration each time the velocity is zero. O A. a(6) = - 6 m/sec , a(4) = 6 m/sec2 O B. a(6) =6 m/sec, a(4)= - 6 m/sec2 O C. a(12) = 72 m/sec, a(8) = 12 m/sec2 O D. a(6) = 0 m/sec, a(4) =0 m/sec