A patient presents to a physician because of a markedly inflamed and painful great toe. Physical examination additionally demonstrates small nodules on the patient's external ear. Aspiration of the metatarsal-phalangeal joint of the affected toe demonstrates needle-shaped, negatively birefringent crystals. Of which of the following are the crystals most likely composed?
Bile pigments Calcium pyrophosphate Cystine Monosodium urate