## Core Concept
The question tests knowledge of parasites that cause intestinal infections and their characteristic effects on the host, specifically regarding the appearance of eggs in stool samples. Bile-stained eggs are indicative of certain parasitic infections.

## Why the Correct Answer is Right
The correct answer, *Ascaris lumbricoides*, lays eggs that are indeed bile-stained. These eggs are typically brown in color due to the bile pigments they have been exposed to in the intestines. *Ascaris lumbricoides* is a large intestinal roundworm that infects humans and can cause intestinal obstruction or respiratory symptoms during larval migration.

## Why Each Wrong Option is Incorrect
* **Option A:** *Enterobius vermicularis* (pinworm) eggs are not bile-stained; they are typically white or transparent and are often found on the perianal skin, especially at night.
* **Option B:** *Trichuris trichiura* (whipworm) eggs have a characteristic barrel shape with bipolar plugs but are not specifically described as bile-stained; they are usually golden-brown.
* **Option D:** *Taenia saginata* (beef tapeworm) eggs are not bile-stained; they are usually described as being brown and having a radially striated outer shell.

## Clinical Pearl / High-Yield Fact
A key clinical point is that the presence of bile-stained eggs in stool is suggestive of an intestinal infection caused by *Ascaris lumbricoides*. This parasite's lifecycle includes migration through the lungs, which can cause significant respiratory symptoms.

## Correct Answer: C. Ascaris lumbricoides