**Core Concept**
Hookworms are intestinal nematodes that infect humans, causing significant morbidity worldwide. They have a complex life cycle involving multiple hosts, with the adult worms residing in the small intestine of their definitive host, where they attach to the mucosa and feed on blood.

**Why the Correct Answer is Right**
The jejunum, the middle portion of the small intestine, is the preferred habitat of hookworms. Adult hookworms attach to the mucosal surface of the jejunum, where they secrete enzymes that break down the host's mucins and facilitate their feeding. This attachment is mediated by the hookworm's buccal capsule, which contains teeth-like structures that allow the worm to anchor itself to the host's mucosa. The jejunum's rich blood supply and optimal pH conditions provide an ideal environment for the hookworms to thrive and multiply.

**Why Each Wrong Option is Incorrect**
**Option B:** The ileum, the final portion of the small intestine, is not the preferred habitat of hookworms. While hookworms may occasionally be found in the ileum, their attachment and feeding activities are primarily centered in the jejunum.
**Option C:** The colon, part of the large intestine, is not a suitable habitat for hookworms. Hookworms are adapted to live in the small intestine, where they can access the necessary nutrients and oxygen to sustain themselves.
**Option D:** The duodenum, the first portion of the small intestine, is not the preferred habitat of hookworms. While hookworms may initially enter the host's body through the duodenum, they quickly migrate to the jejunum, where they attach and begin their feeding activities.

**Clinical Pearl / High-Yield Fact**
Hookworms are a significant public health problem in many developing countries, causing iron-deficiency anemia, malabsorption, and other complications. The primary mode of transmission is through fecal-oral contact with contaminated soil or water.

**✓ Correct Answer: A. Jejunum**