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: Dental
All of them are usually seen as an opportunistic infection in AIDS except: 
Select and explain. 
A. Candidiasis, B. Kaposi's sarcoma, C. Rubella, D. Cytomegalovirus infection
C: Rubella
Answer: C: Rubella 
Explanation: None