18. A charged capacitor connected to a resistor and a switch, which is open for t＜0. After the switch isclosed at t=0, the capacitor C is discharged through the resistor R. The energy stored in the capacitordecreases with time as it discharges. After how many time constants is this stored energy one eighth ofits initial value? (ln2=0.693)
(A) 0.347 RC
(B) 0.693 RC
(C) 1.040 RC
(D) 1.386 RC
(E) 2.079 RC