This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Microbiology
Cyst stage is absent in 
Select and explain. 
A. Dientamoeba fragilis, B. Entamoeba coli, C. Entamoeba histolytica, D. All of the above
A: Dientamoeba fragilis
Answer: A: Dientamoeba fragilis 
Explanation: Dientamoeba fragilis is a parasite that lives in the large intestine of people. 
This protozoan parasite produces trophozoites; cysts have not been identified. 
The intestinal infection may be either asymptomatic or symptomatic. 
Many infected people do not have any symptoms. 
The most common symptoms are diarrhea and abdominal pain. 
Symptoms also can include loss of appetite, weight loss, nausea, and fatigue. 
The infection does not spread from the intestine to other parts of the body.
Entamoeba coli and Entamoeba histolytica both have cyst stage.​

Ref :https://www.cdc.gov/parasites/dientamoeba/index.html