**Core Concept**
The underlying principle being tested is the life cycle of *Toxoplasma gondii*, a parasitic protozoan. *Toxoplasma gondii* has a complex life cycle involving multiple hosts. The infective form is crucial for initiating infection in humans and other intermediate hosts.

**Why the Correct Answer is Right**
The correct answer is related to the oocyst or cyst form, which is highly infectious. *Toxoplasma gondii* oocysts are shed in the feces of infected cats, the definitive host, and can infect intermediate hosts, including humans, through contaminated food or water.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately represent the infective form of *Toxoplasma gondii*.
**Option B:** Similarly, this option is incorrect as it is not the primary infective form.
**Option D:** This option is also incorrect for the same reason.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that *Toxoplasma gondii* infection can have severe consequences in immunocompromised individuals and pregnant women, highlighting the importance of proper hygiene and food handling practices to prevent infection.

**Correct Answer:** C. Oocyst