**Core Concept**
The question is testing the knowledge of a specific vitamin that plays a crucial role in preventing infections. This vitamin is essential for the proper functioning of the immune system and has been widely used as a supplement to prevent and treat infections.

**Why the Correct Answer is Right**
The correct answer is Vitamin C, which is known for its anti-inflammatory and antioxidant properties. It is involved in the synthesis of collagen, absorption of iron, and the proper functioning of the immune system. Vitamin C also has a role in the production of white blood cells, which are essential for fighting off infections. The mechanism of action of Vitamin C involves the stimulation of the production of interferon, which is a protein that helps to prevent the replication of viruses.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because Vitamin A is primarily known for its role in vision, immune function, and reproduction, but it is not typically classified as an anti-infective vitamin.
**Option B:** Incorrect because Vitamin E is an antioxidant that helps protect cells from damage, but it does not have a direct role in preventing infections.
**Option C:** Incorrect because Vitamin K is essential for blood clotting and bone health, but it does not have anti-infective properties.

**Clinical Pearl / High-Yield Fact**
It's essential to note that Vitamin C deficiency can lead to scurvy, a condition characterized by fatigue, malaise, and poor wound healing. This highlights the critical role of Vitamin C in maintaining overall health and preventing infections.

**Correct Answer: A. Vitamin C**