A Zener diode
A. has a high forward voltage rating.
B. has a sharp breakdown at low reverse voltage.
C. has a negative resistance.
D. none of the above.

Hint: To solve this question, we have to remember some basic points of the mechanism of Zener diode. Zener diode is like an ordinary P-N junction diode except that it is properly doped so as to have a sharp breakdown voltage.
There are many two-terminal devices, which have a single P-N junction. Zener diode is one of such two-terminal devices. Zener diodes are operated in reverse breakdown because they have very stable breakdown voltage.

Complete step-by-step solution:

We know that,
The critical value of the voltage, at which the breakdown of a P-N junction diode occurs is called the breakdown voltage.
Applying negative potential to the anode and positive potential to cathode reverse bias the Zener diode. and breakdown occurs at low reverse voltage and breakdown voltage is sharp.
The V-I characteristics for Zener diode are shown below,

Also, the negative resistance characteristic of Zener diodes in the range of avalanche breakdown region. But Zener diodes have a positive resistance because if we increase the current, the voltage developed will increase.
Hence, we can say that the Zener diode has a sharp breakdown at low reverse voltage.
Therefore, the correct answer is an option (B).

Note: The depletion area extends under a very high reverse voltage, and the potential barrier increases, resulting in a very high electric field in the junction. This is known as the Zener effect. The breakdown occurs at reverse voltage, called the breakdown voltage, at a particular and constant value. It is observed that the voltage to breakdown occurs at around $3 \times {10^7}$ V/m electric field strength.