This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Disorders of menstruation, Subject name: Gynaecology & Obstetrics
Primary amenorrhea is absence of menstruation by the age of 
Select and explain. 
A. 13 years, B. 15 years, C. 16 years, D. 18 years
C: 16 years
Answer: C: 16 years 
Explanation: Primary amenorrhea refers to the failure of the onset of menstruation beyond the age of 16 years regardless of the development of secondary sexual characters Ref: Shaw Gynecology 17 e pg 141.