The correct answer is: D. R-L-C circuit.
A double energy transient occurs in an R-L-C circuit when the current through the inductor and the voltage across the capacitor are both maximum. This occurs when the switch in the circuit is closed, and the current begins to flow through the inductor. The inductor stores energy in its magnetic field, and the capacitor stores energy in its electric field. As the current flows through the inductor, it creates a magnetic field that opposes the current. This causes the current to decrease, and the energy stored in the magnetic field is transferred to the capacitor. The capacitor then stores this energy in its electric field. As the voltage across the capacitor increases, it creates an electric field that opposes the voltage. This causes the voltage to decrease, and the energy stored in the electric field is transferred back to the inductor. The inductor then stores this energy in its magnetic field. This process continues until the current and voltage reach their maximum values.
In a purely inductive circuit, there is no capacitor, so there is no energy stored in the electric field of the capacitor. This means that the current through the inductor will continue to increase until it reaches its maximum value. The voltage across the inductor will also continue to increase until it reaches its maximum value. However, there will be no double energy transient in this circuit.
In an R-C circuit, there is no inductor, so there is no energy stored in the magnetic field of the inductor. This means that the voltage across the capacitor will continue to increase until it reaches its maximum value. The current through the capacitor will also continue to increase until it reaches its maximum value. However, there will be no double energy transient in this circuit.
In an R-L-C circuit, there is both an inductor and a capacitor. This means that there is energy stored in both the magnetic field of the inductor and the electric field of the capacitor. This causes the current through the inductor and the voltage across the capacitor to both reach their maximum values at the same time. This is known as a double energy transient.