This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Genito Urinary System, Subject name: Radiology
Which of the following is a radiolucent stone? 
Select and explain. 
A. Uric acid, B. Oxalate, C. Cysteine, D. Triple phosphate
A: Uric acid
Answer: A: Uric acid 
Explanation: Ans: a (Uric acid) Ref: Bailey and Love, 24th ed, p. 1317Pure uric acid stones are radiolucent and appear in an excretory urogram as filling defects.Uric acid stones if contain calcium, will cast a faint radiological shadow.Examples for radiolucent stones* Uric acid* Dihydroxy adenine* Orotic acid* Xanthine* Allopurinol* Triamterine and Indinavir induced stones.