13. In the circuit shown above, the capacitor C is first charged by throwing switch S to the left, then discharged by throwing S to the right. The time constant for discharge could be increased by which of the following?
(A) Placing another capacitor in parallel with C
(B) Placing another capacitor in series with C
(C) Placing another resistor in parallel with the resistor R
(D) Increasing battery emf E
(E) Decreasing battery emf E