## Core Concept
The question tests knowledge of parasitic infections, specifically how certain parasites enter the human body. Some parasites gain entry through the skin, which is a critical aspect of their life cycle.

## Why the Correct Answer is Right
The correct answer, **Hookworm**, penetrates the human body through the skin. Hookworms are a type of nematode (roundworm) that infect humans. The larvae of hookworms, typically found in contaminated soil, penetrate the skin when a person walks barefoot on infected ground. This penetration is the initial step in their lifecycle within a human host, leading to intestinal infection.

## Why Each Wrong Option is Incorrect
* **Option A: Plasmodium** - This parasite, which causes malaria, is transmitted through the bite of an infected Anopheles mosquito, not through skin penetration in the manner described for hookworms.
* **Option B: Giardia** - Giardiasis is caused by Giardia lamblia, a protozoan parasite. It is usually acquired through the fecal-oral route, often via contaminated water, not through skin penetration.
* **Option D: Ascaris** - While Ascaris lumbricoides (the roundworm) does infect humans, it does not penetrate the skin to enter the body. Instead, it is ingested in its egg form, typically through contaminated food or water.

## Clinical Pearl / High-Yield Fact
A key point to remember is that hookworm infection can cause cutaneous larva migrans, a condition characterized by a serpiginous, itchy skin lesion that represents the larva's migration through the skin before it penetrates and continues its lifecycle internally.

## Correct Answer: C. Hookworm.