Pfiesteria is a protozoan that produces a toxin harmful to humans. Here's why:
1. Protozoans are single-celled organisms that can be found in water environments.
2. Pfiesteria is a type of protozoan that has been associated with harmful algal blooms.
3. These blooms can release toxins into the water, which can be harmful to marine life and humans.
4. Pfiesteria has been known to cause fish kills and can also impact human health if individuals come into contact with contaminated water.
Therefore, the correct answer is:
O e. protozoan
