The device that can act as a complete electronic circuit is

An amplifier has a voltage gain $A_v = 1000$. The voltage gain in $dB$ is...........

Consider the following statements:
Statement $(A)$: The resistance of an ideal diode in forward biased condition is zero.
Statement $(B)$: In a half-wave rectifier,the load current flows only for every half cycle of the input signals.
Statement $(C)$: In the breakdown region,a Zener diode behaves as a constant voltage source.

Which of the following $p-n$ junction devices is not used in reverse bias?

Which of the following figures correctly shows the phase relation between the input signal and the output signal of a common-emitter transistor amplifier?

In which of the following cases is the junction diode $NOT$ in reverse bias?