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
Which one of the following is true about Giardia? 
Select and explain. 
A. Cyst is infective to man, B. Inhabits duodenum and upper jejunam, C. Tropozoite has 2 flagella, D. Both 'a' and 'b'
D: Both 'a' and 'b'
Answer: D: Both 'a' and 'b' 
Explanation: The flagellate protozoan Giardia intestinalis (previously known as G lamblia), its causative agent, is the most common protozoal intestinal parasite isolated worldwide. Ingestion of as few as 10 Giardia cysts may be sufficient to cause infection. The trophozoite also contains 4 pairs of flagella, directed posteriorly, that aid the parasite in moving. It inhabits duodenum and upper jejunam.