Protozoa can be found in which of the following habitats?

Protozoa are highly versatile microorganisms that can thrive in a range of habitats, particularly in aquatic environments. Fresh and saltwater environments are particularly conducive to the existence of protozoa due to the availability of moisture and nutrients. In freshwater systems like ponds, lakes, and streams, protozoa play essential roles in nutrient cycling and as part of the food web. Similarly, saltwater environments, such as oceans and estuaries, also support diverse protozoan communities.

While protozoa may occasionally be found in other habitats like deserts, forests, or mountains, these environments do not generally provide the continuous moisture and nutrient availability that protozoa require for survival and reproduction. Therefore, the rich ecosystems found in both fresh and saltwater environments are crucial for the presence of protozoa, making this the correct answer.