This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Virology, Subject name: Microbiology
A child has mononucleosis-like symptoms yet the test for mononucleosis and the EBV titers are negative. One of the causes of heterophile-negative mononucleosis is 
Select and explain. 
A. Cytomegalovirus, B. Herpes simplex virus, C. Varicella-zoster virus, D. Adenovirus
A: Cytomegalovirus
Answer: A: Cytomegalovirus 
Explanation: Infectious mononucleosis caused by cytomegalovirus (CMV) is clinically difficult to distinguish from that caused by Epstein-Barr virus. Lymphocytosis is usually present with an abundance of atypical lymphocytes. CMV-induced mononucleosis should be considered in any case of mononucleosis that is heterophil-negative and in patients with fever of unknown origin.