A variable power supply drives a time-dependent current through a circuit element. The current increases linearly from \(0\) to \(I_0\) between \(t = 0\) and \(t = t_1\), and then remains constant at \(I_0\) from \(t = t_1\) to \(t = 2t_1\). Which of the following graphs best represents the total charge \(Q\) that has passed through the circuit element as a function of time \(t\)?