Small kidneys (1318/1700)

An elder man who has anorexia, prostate symptoms and HTN. There are small kidneys on US.
What is the dx?
a. Hypertensive renal disease
b. Prostate ca
c. BPH

answer: A

B and C will cause obstruction with hydronephrosis/acute renal failure, not chronic renal failure with small kidneys.