In a circuit the phase difference between the alternating current and the source voltage is $${\pi \over 2}$$. Which of the following cannot be the elements of the circuit?

The impedance of a series LCR circuit is -

When an alternating voltage E = E_o sin $$\omega$$t is applied to a circuit, a current $$I = {I_o}\sin \left( {\omega t + {\pi \over 2}} \right)$$ flows through it. The average power dissipated in the circuit is

The voltage across a resistor, an inductor, and a capacitor connected in series to an ac source are 20 V, 15 V and 30 V respectively. The resultant voltage in the circuit is