**Core Concept**
The patient's presentation is suggestive of biliary obstruction, which is a classic symptom complex of liver fluke infestation. The liver fluke, *Clonorchis sinensis*, is a parasitic flatworm that inhabits the bile ducts and can cause biliary obstruction, cholangitis, and secondary biliary cirrhosis.

**Why the Correct Answer is Right**
The patient's symptoms, including upper right quadrant abdominal pain, jaundice, and dark urine, are consistent with biliary obstruction. The liver fluke *Clonorchis sinensis* is a common parasite in the Far East and can cause these symptoms by obstructing the bile ducts. The parasite's eggs are excreted in the feces and can hatch in fresh water, allowing the larvae to penetrate human skin.

**Why Each Wrong Option is Incorrect**
* **Option A:** *Ascaris lumbricoides* is a large intestinal parasite that can cause intestinal obstruction, but it is not typically associated with biliary obstruction or liver disease.
* **Option B:** *Entamoeba histolytica* is a protozoan parasite that can cause intestinal amoebiasis, but it is not typically associated with biliary obstruction or liver disease.
* **Option C:** *Opisthorchis viverrini* is another liver fluke that can cause biliary obstruction, but it is more commonly found in Southeast Asia than in the Far East.

**Clinical Pearl / High-Yield Fact**
The "rice-water stool" of *Ascaris lumbricoides* infection is a classic symptom complex that can be remembered using the mnemonic "rice-water stool = *Ascaris*".

**Correct Answer:** C.