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
[{'content': '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 \nSelect and explain. \nA. Cytomegalovirus, B. Herpes simplex virus, C. Varicella-zoster virus, D. Adenovirus', 'role': 'user'}, {'content': 'Answer: A \nExplanation: 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.', 'role': 'assistant'}]