The law of motion of a body moving along a straight line is \(x=\frac{1}{2} v t, x\) being its distance from a fixed point on the line at time \(t\) and \(v\) is its velocity there. Then
(A) acceleration \(\mathrm{f}\) varies directly with \(\mathrm{x}\)
(B) acceleration \(f\) varies inversely with \(x\)
(C) acceleration \(\mathrm{f}\) is constant
(D) acceleration \(\mathrm{f}\) varies directly with \(\mathrm{t}\)