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

In which of the following circuits is the junction reverse biased?

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.

The resultant voltage gain in a series combination of two or more amplifiers is .......

In an oscillator,if $\beta$ is the feedback factor and $A$ is the gain of the amplifier,then sustained oscillations are obtained when:

Select the correct statements from the following: