**Core Concept**
The question is testing the student's knowledge of the specific strain of E. coli responsible for traveler's diarrhea, a common gastrointestinal disorder affecting individuals who travel to developing countries. **Enterotoxigenic E. coli (ETEC)** is a pathogenic strain of E. coli that adheres to the intestinal mucosa and produces heat-stable and heat-labile enterotoxins, leading to watery diarrhea.

**Why the Correct Answer is Right**
ETEC is the most common cause of traveler's diarrhea, accounting for approximately 70% of cases. This strain is typically acquired through contaminated food or water, and its pathogenesis involves the colonization factor antigens (CFAs) that facilitate adherence to the intestinal mucosa. The heat-stable and heat-labile enterotoxins produced by ETEC stimulate the small intestine to secrete large amounts of water and electrolytes, resulting in the characteristic symptoms of traveler's diarrhea.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because **Enteropathogenic E. coli (EPEC)** is primarily associated with infantile diarrhea in developing countries, not traveler's diarrhea.
**Option B:** **Enterohemorrhagic E. coli (EHEC)** is known for causing hemorrhagic colitis, often leading to hemolytic uremic syndrome (HUS), and is not typically associated with traveler's diarrhea.
**Option C:** **Enteroinvasive E. coli (EIEC)** is a rare cause of diarrhea that resembles shigellosis, characterized by dysentery and a higher frequency of systemic complications.

**Clinical Pearl / High-Yield Fact**
It's essential for travelers to maintain good hygiene practices, such as frequent handwashing and avoiding undercooked food and water, to reduce their risk of acquiring ETEC-induced traveler's diarrhea.

**Correct Answer:** C. Enterotoxigenic E. coli (ETEC)