A particle of mass \(m\) moves in the \(xy\)-plane along the horizontal line \(y = d\) in the positive \(x\)-direction with a speed given as a function of time \(t\) by \(v(t) = C t^2\), where \(C\) is a positive constant. Which of the following expressions represents the magnitude of the rate of change of the particle's angular momentum about the origin, \(\dfrac{dL}{dt}\), as a function of time?