**Core Concept**
Horizontal gene transfer is the process by which bacteria share genetic material, bypassing vertical inheritance from parent to offspring. This phenomenon is crucial for bacterial adaptation, evolution, and the spread of antibiotic resistance.

**Why the Correct Answer is Right**
Transformation is a natural method of horizontal gene transfer among bacteria, where free DNA molecules from the environment are taken up by the bacterial cell. This process occurs when a bacterium accidentally ingests DNA fragments from its surroundings, which can then integrate into its genome. The uptake of DNA is often facilitated by the bacterial cell's outer membrane, and the process is influenced by factors such as the presence of divalent cations.

**Why Each Wrong Option is Incorrect**
**Option A:** Electroporation is a laboratory technique used to introduce DNA into bacterial cells using an electric pulse, but it is not a natural method of horizontal gene transfer.
**Option B:** Transduction involves the transfer of bacterial DNA from one cell to another through a viral vector (a bacteriophage), which is not a direct, natural process between bacteria.
**Option D:** Conjugation is a natural process of horizontal gene transfer where bacteria directly transfer DNA from one cell to another through a specialized structure called a conjugation pilus, but it involves direct cell-to-cell contact.
**Option E:** Mutation refers to a change in the DNA sequence of an organism, which is not a method of gene transfer between bacteria.

**Clinical Pearl / High-Yield Fact**
Remember that transformation is a key mechanism by which bacteria can acquire new genetic traits, including antibiotic resistance, which can have significant implications for human health.

**Correct Answer:** C. Transformation