The correct answer is option 'C', which states that the Sporozoa are all internal parasites that typically have an infective cyst stage in their life cycle. An example of Sporozoa is the genus Plasmodium, which causes malaria.

Explanation:
The Sporozoa is a phylum of parasitic protozoans that belong to the kingdom Protista. These organisms are characterized by their internal parasitic lifestyle and the presence of a spore-like stage called a sporozoite. Sporozoans are typically found in animals, including humans, and have complex life cycles that involve both sexual and asexual stages.

- Sporozoa as internal parasites:
- The Sporozoa are all internal parasites, meaning they live inside the host organism.
- They require a host to complete their life cycle and reproduce.
- Sporozoans are commonly found in the blood, tissues, or organs of their hosts.

- Infective cyst stage:
- The life cycle of many Sporozoa includes an infective cyst stage.
- A cyst is a protective structure that allows the organism to survive harsh conditions and facilitates transmission to a new host.
- The cyst stage is often resistant to environmental changes and can remain viable outside the host for extended periods.

- Genus Plasmodium and malaria:
- Plasmodium is a genus of Sporozoa that includes several species known to cause malaria.
- Malaria is a potentially life-threatening disease transmitted through the bite of infected female Anopheles mosquitoes.
- When an infected mosquito bites a human, it injects sporozoites, the infective stage of Plasmodium, into the bloodstream.
- The sporozoites travel to the liver, where they invade liver cells and multiply asexually, forming merozoites.
- The merozoites are released into the bloodstream, where they invade red blood cells and continue to multiply.
- This multiplication cycle causes the characteristic symptoms of malaria, including fever, chills, and anemia.
- Some merozoites develop into sexual forms called gametocytes, which can be taken up by mosquitoes during a blood meal, completing the life cycle.

In conclusion, the Sporozoa are internal parasites that typically have an infective cyst stage in their life cycle. The genus Plasmodium, which causes malaria, is an example of Sporozoa.