**Core Concept**
The question is testing the student's knowledge of helminth infections, specifically their clinical manifestations and the organs they typically affect. The correct answer will be a type of helminth that primarily causes gastrointestinal symptoms without involving the lungs.

**Why the Correct Answer is Right**
The correct answer is the hookworm. Hookworms (Ancylostoma duodenale and Necator americanus) are small, blood-feeding nematodes that primarily infect the small intestine. They cause gastrointestinal symptoms such as abdominal pain, diarrhea, and weight loss, but they do not typically cause lung involvement. This is because they do not migrate to the lungs during their life cycle, unlike other types of helminths such as Ascaris lumbricoides.

**Why Each Wrong Option is Incorrect**
**Option A:** Ascaris lumbricoides is a type of roundworm that can cause gastrointestinal symptoms, but it also commonly migrates to the lungs during its life cycle, causing respiratory symptoms such as coughing and wheezing.

**Option B:** Trichuris trichiura (whipworm) is another type of helminth that infects the large intestine. While it can cause gastrointestinal symptoms, it also has a migratory phase that involves the lungs.

**Option C:** Strongyloides stercoralis is a type of helminth that can cause gastrointestinal symptoms, but it also has a migratory phase that involves the lungs, and can even cause autoinfection and hyperinfection.

**Clinical Pearl / High-Yield Fact**
It's worth noting that hookworm infections are often asymptomatic, and may only be detected through stool examination. This is because the worms primarily feed on blood in the small intestine, and do not cause significant inflammation or damage to the intestinal lining.

**Correct Answer:** D. Hookworms are the primary helminths that cause gastrointestinal symptoms without lung involvement.