An air-filled parallel-plate capacitor with plate area \(A\) and initial plate separation \(d_0\) is connected across an ideal battery that maintains a constant potential difference \(V_0\). While remaining connected to the battery, the separation \(d\) between the plates is slowly and continuously increased from \(d_0\) to \(3d_0\). Which of the following best describes the graph of the magnitude of charge \(Q\) on the positive plate as a function of plate separation \(d\)?