This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: general microbiology, Subject name: Microbiology
Which of the following are a Bacteria taxonomically? 
Select and explain. 
A. Chlamydia, B. Rickettsia, C. Mycoplasma, D. Prion
A: Chlamydia
Answer: A: Chlamydia 
Explanation: Chlamydiae are obligate intracellular bacteria belonging to genus Chlamydia, in family Chlamydiaceae, under order Chlamydiales Ref: Textbook of Microbiology; Ananthanarayan and Paniker; 9th edition; Pg no: 415