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: Medicine
An 80 year old asymptomatic woman was detected to have a monoclonal spike on serum electrophoresis (IgG levels 1.5 g/dl). 1: one marrow revealed plasma cells of 8%. The most likely diagnosis is - 
Select and explain. 
A. Multiple myeloma, B. Indolent myeloma, C. Monoclonal gammopathy of unknown significance, D. Waldenstorrn's macroglobulinemia
C: Monoclonal gammopathy of unknown significance
Answer: C: Monoclonal gammopathy of unknown significance 
Explanation: None