This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Infertility, Subject name: Gynaecology & Obstetrics
A male with azoospermia. On examination size of testis is normal. FSH and testosterone levels are within normal limits. Most probable cause is: 
Select and explain. 
A. Non-descended testis, B. Klinefelter's syndrome, C. Kallmann's syndrome, D. VAS obstruction
D: VAS obstruction
Answer: D: VAS obstruction 
Explanation: Normal levels of FSH with azoospermia suggests obstructive lesions in the vas or epididymis. High FSH and LH may indicate primary gonadal failure-testicular Dysfunction. Low level of FSH and LH suggest hypogonadotropic hypogonadism. Shaw's Textbook of Gynaecology 16th edition page no 244