**Core Concept**
Bacteria acquire restriction endonucleases through horizontal gene transfer, which is a process where bacteria share genetic material with each other. This transfer of genetic material allows bacteria to acquire new enzymes that can cleave foreign DNA, providing an additional layer of defense against invading viruses and other bacteria.

**Why the Correct Answer is Right**
When a bacterium acquires a restriction endonuclease through horizontal transfer, it can recognize and cleave foreign DNA, including that of invading viruses (phages). This is because restriction endonucleases are enzymes that cleave DNA at specific recognition sites. By acquiring a new restriction endonuclease, the bacterium can expand its range of target DNA sequences, making it more resistant to phage infections. This process is an example of a key mechanism by which bacteria defend themselves against viral infections.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not accurately describe the result of a bacterium acquiring a restriction endonuclease through horizontal transfer.
* **Option B:** This option is incorrect because it is too vague and does not accurately reflect the specific consequences of acquiring a restriction endonuclease.
* **Option C:** This option is incorrect because it is not directly related to the consequences of acquiring a restriction endonuclease.

**Clinical Pearl / High-Yield Fact**
It is worth noting that restriction endonucleases are often used in molecular biology techniques, such as PCR and DNA sequencing, due to their ability to cleave DNA at specific recognition sites. This highlights the importance of these enzymes in both bacterial defense mechanisms and laboratory applications.

**Correct Answer: A. Increased resistance to viral infections**