**Core Concept**
The question is testing knowledge of parasitology, specifically the life cycles of various parasites. The life cycle of a parasite refers to the stages of development it undergoes to complete its reproductive cycle, which can involve one or more hosts.

**Why the Correct Answer is Right**
The correct answer involves a parasite that requires three different hosts to complete its life cycle, a process known as heteroxenous development. This complexity allows the parasite to increase its chances of survival and reproduction.

**Why Each Wrong Option is Incorrect**
**Option A:** This choice is incorrect because it typically involves a different number of hosts.
**Option B:** Similarly, this option does not fit the three-host criterion.
**Option D:** This choice also does not match the described life cycle.

**Clinical Pearl / High-Yield Fact**
Parasites with complex life cycles often have evolved unique adaptations to ensure their survival, making their diagnosis and treatment challenging. Understanding these life cycles is crucial for effective public health interventions.

**Correct Answer:** D. Schistosoma.