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: Gynaecology & Obstetrics
The commonest cause of primary Amenorrhoea is: 
Select and explain. 
A. Genital tuberculosis, B. Ovarian dysgenesis, C. Mullerian duct anomalies, D. Hypothyroidism
B: Ovarian dysgenesis
Answer: B: Ovarian dysgenesis 
Explanation: Most common cause of Primary Amenorrhea = Gonadal dysgenesis/ovarian dysgenesis
2nd most common cause of Primary Amenorrhea = Mullerian agenesis (Mayer Rokitansky Kuster Hauser Syndrome) 

“Mullerian agenesis is a relatively common cause of primary amenorrhea, more frequent than congenital androgen insensitivity and second only to gonadal dysgenesis”

 3rd most common cause is testicular feminizing syndrome.