## Core Concept
Bacteriophages, commonly known as phages, are **viruses that infect bacteria**. They are composed of genetic material, either DNA or RNA, enclosed in a protein coat. Phages are highly specific to their bacterial hosts.

## Why the Correct Answer is Right
The correct answer, not explicitly provided, likely relates to a specific characteristic of bacteriophages. Generally, phages are known for their **high specificity to bacterial hosts**, their **role in transduction** (transferring bacterial DNA from one bacterium to another), and their **potential as therapeutic agents** against bacterial infections.

## Why Each Wrong Option is Incorrect
- **Option A:** Without the specific details of option A, it's challenging to provide a direct explanation. However, if option A suggested that phages infect human cells, it would be incorrect because phages are **specific to bacterial cells**.
- **Option B:** Similarly, without specifics, if option B proposed that phages are a type of bacteria, it would be incorrect because phages are **viruses**, not bacteria.
- **Option C:** If option C stated something incorrect about the composition or function of phages (e.g., they contain both DNA and RNA), it would be wrong because phages typically have **either DNA or RNA**, not both, as their genetic material.
- **Option D:** If option D suggested phages are non-specific, this would be incorrect because one of the defining features of phages is their **high specificity** for certain bacterial strains.

## Clinical Pearl / High-Yield Fact
A significant clinical application of bacteriophages is their use as **therapeutic agents** to treat bacterial infections, especially those caused by **multi-drug resistant bacteria**. This approach is known as phage therapy. Understanding the specificity and mechanism of action of phages is crucial for their application in medicine.

## Correct Answer Line
**Correct Answer: D.**