## Core Concept
The question assesses knowledge of parasites associated with malignancy. Certain parasites are known to contribute to the development of cancer in humans, often through chronic infection and inflammation. The most well-known associations include **Schistosoma** species with bladder cancer and **Helicobacter pylori** with gastric cancer, but the question pertains to a list of parasites.

## Why the Correct Answer is Right
The correct answer, **Opisthorchis viverrini**, is indeed associated with cholangiocarcinoma, a type of bile duct cancer. **Schistosoma** species, particularly **S. haematobium**, are linked to bladder cancer. **Human T-cell lymphotropic virus 1 (HTLV-1)**, while not a parasite itself, is sometimes confused in lists due to its association with adult T-cell leukemia/lymphoma, but there's no direct parasitic link here; however, **Toxoplasma gondii** has been studied for potential associations with certain malignancies, though evidence is less direct compared to others.

## Why Each Wrong Option is Incorrect
- **Option A:** If listed as a causative agent, it's incorrect because the actual association might not be as strong or direct as others listed, or it might be incorrectly attributed.
- **Option B:** Incorrect if this option represents a known causative agent of malignancy, as the question seeks the exception.
- **Option C:** If this option represents **Opisthorchis viverrini**, it's actually correct that it's associated with malignancy, making it not the exception.
- **Option D:** If **Toxoplasma gondii** or another parasite not commonly associated with cancer causation is listed here and chosen as the correct answer, it implies that the other options have established links to malignancy.

## Clinical Pearl / High-Yield Fact
A key point to remember is that **Opisthorchis viverrini** and **Schistosoma** species are classified as carcinogenic to humans by the International Agency for Research on Cancer (IARC), emphasizing their role in causing malignancy.

## Correct Answer: D. Toxoplasma gondii