The circuit shown in the figure is used to charge the capacitor C alternately from two current sources as indicated. The switches S1 and S2 are mechanically coupled and connected as followFor 2nT ≤ t < (2n + 1)T, (n = 0, 1, 2, ...) S1 to P1 and S2 to P2For (2n + 1) T ≤ t < (2n + 2)T, (n = 0, 1, 2, ...) S1 to Q1 and S2 to Q2 Assume that the capacitor has zero initial charge. Given that u(t) is a unit step function, the voltage Vc(t) across the capacitor is given be

• A. (- 1)n tu(t - nT)
• B. u(t) + 2 (-1)n u(t - nT)
• C. tu(t) + 2 (-1)n (t - nT) u(t - nT)
• D. [0.5 - e-(t - 2nT) + 0.5e-(t - 2nT - T) ]