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 is intracellular? 
Select and explain. 
A. Virus, B. Chlamydia, C. Mycoplasma, D. Rickettsia
A: Virus
Answer: A: Virus 
Explanation: viruses are obligate intracellular parasites Viruses do not have cellular organizations They contain only one type of nucleic acid, either DNA Or RNA They are obligate intracellular parasites they lack enzymes necessary for synthesis and replication They multiply by a complex process and not by binary fission They are unaffected by antibacterial antibiotics Ref: Ananthanarayan & paniker's Textbook of Microbiology 9th edition pg no 427