**Core Concept**
Hookworms are a type of intestinal parasite that infect humans, causing hookworm disease or ancylostomiasis. They thrive in the small intestine, where they feed on the host's blood.

**Why the Correct Answer is Right**
Hookworms secrete an anticoagulant that prevents blood clotting, allowing them to feed on the host's blood without being detected. This anticoagulant is secreted by the hookworm's mouth and is thought to be a key factor in their ability to thrive in the host's small intestine. The anticoagulant works by inhibiting the conversion of fibrinogen to fibrin, preventing the formation of blood clots.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not relevant to the question. Hookworms do not thrive on glucose.
* **Option B:** This option is incorrect because hookworms do not thrive on amino acids. While they may require amino acids for growth and development, their primary source of nutrition is blood.
* **Option C:** This option is not correct. Hookworms do not thrive on lipids. While they may require lipids for energy, their primary source of nutrition is blood.

**Clinical Pearl / High-Yield Fact**
Hookworms are a significant public health problem in many parts of the world, particularly in tropical and subtropical regions. They can cause significant morbidity and mortality, particularly in children and pregnant women.

**Correct Answer: D. Blood**