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
A patient presents with diarrhoea. analysis of stool on wet mount shows mobile protozoa without RBCs and pus cells. The diagnosis is - 
Select and explain. 
A. Balantidium coil, B. Giardiasis, C. Trichomonas hominis, D. Entamoeba histolytica
B: Giardiasis
Answer: B: Giardiasis 
Explanation: Ans. is 'b' i.e., Giardiasis . Mobile protozoa with absence of RBC's and pus cells in stools in a patient with diarrhoea suggests giardiasis. . In balantidum cob and entomoeba histolytica infections, pus cells and RBC's will be present in stools. Trichomonas hominis is considered as non-pathogenic