This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Kidney & Ureturs, Subject name: Surgery
Harder stone with less satisfactory result in ESWL is 
Select and explain. 
A. Oxalate, B. Phosphate, C. Urate, D. Cystine stones
D: Cystine stones
Answer: D: Cystine stones 
Explanation: Ans. (d) Cystine StonesRef Bailey and Love 27th Edition, Page 1408Extra Corporeal Shock Wave Lithotripsy:* Shock waves generated and focused on the stones.* Methods of Shock Wave Generation:# Spark Gap# Electromagnetic# Piezo Electric# Micro Expulsive* Cardiac arrhythmias can happen in cases of Spark Gap generated waves* ESWL is indicated for stones upto 1.5cm in kidney* Prophylactic antibiotics are advised.* Relatively resistant stone is CYSTINE due to its hardness.* Contraindications: Pregnancy and Oral Anticoagulant drug consuming patients* Steinstrasse - Stone street is collection of stone fragments in distal ureter after breaking by ESWL.