单选题-|||-已知某质点的运动学方程为-|||-overrightarrow (r)=3(t)^4overrightarrow (i)+(2(t)^2+10)overrightarrow (j)+5toverrightarrow (k), 式中t以s计,式-|||-中r以m计,则 t=2s 时,质点的瞬时加速度为-|||-()()-|||-A. overrightarrow (i)+4overrightarrow (j)m/(s)^2-|||-B. /(s)^2-|||-C. overline (i)+24overline (j)m/(s)^2-|||-D. overline (j)+8overline (j)m/(s)^2