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 7 year old presented with intermittent abdominal cramps, loose stool and on stool examination eggs of size 100 m are seen, which is not the cause ? 
Select and explain. 
A. Fasciola gigantica, B. Echinostoma iliocanum, C. Gastrodiscoides hominis, D. Opisthorcis viverni
D: Opisthorcis viverni
Answer: D: Opisthorcis viverni 
Explanation: Ans. is. 'd' i.e., Opisthorcis viverni Eggs of Opisthorcis viverni have size very much less than 100 m