## Core Concept
A tandem bullet, also known as a "tandem" or "piggyback" bullet, refers to a type of ammunition where two projectiles are stacked together in a single cartridge. This configuration is designed to increase the effectiveness of the ammunition by allowing two bullets to be fired from a single shot.

## Why the Correct Answer is Right
In a tandem bullet, there are indeed **two bullets** that come out of the gun when it is fired. The design allows for the first bullet to potentially dislodge or expand upon impact, while the second bullet continues to travel, potentially causing additional damage. This mechanism is utilized in specific applications, such as in hunting or tactical situations, where increased stopping power or penetration is desired.

## Why Each Wrong Option is Incorrect
* **Option A:** is incorrect because it suggests only one bullet is fired, which contradicts the fundamental design and purpose of a tandem bullet.
* **Option B:** is incorrect because it implies more than two bullets are fired, which is not characteristic of a tandem bullet setup.
* **Option D:** is incorrect because it suggests a variable or unspecified number of bullets, which does not accurately describe the consistent design of a tandem bullet.

## Clinical Pearl / High-Yield Fact
A key point to remember is that tandem bullets are designed for specific applications and their use can be subject to legal and ethical considerations, especially in hunting and military contexts. Understanding the mechanics and purposes of such ammunition can be crucial for professionals in fields related to ballistics and forensic science.

## Correct Answer Line
**Correct Answer: C. 2.**