The answer is d-Presence of amorphous urate in urine.

Urine pH is a measure of the acidity or alkalinity of urine. The normal range of urine pH is 4.5 to 8.0, with an average of 6.0. Alkaline urine pH is defined as a pH greater than 7.0. Alkaline urine can be seen in various conditions, including urinary tract infections, bilirubin due to jaundice, presence of calcium oxalate crystals in urine, and presence of amorphous urate in urine.

Amorphous urate is a type of crystal that can be found in urine. It is composed of uric acid and other substances, such as calcium and magnesium. Amorphous urate crystals are commonly seen in alkaline urine, with a pH greater than 7.0. This is because uric acid is more soluble in acidic urine, with a pH less than 7.0. When the urine becomes alkaline, uric acid precipitates out of solution and forms crystals.

Therefore, the presence of amorphous urate in urine is a common cause of alkaline urine pH. Other causes of alkaline urine pH include certain medications, such as antacids and diuretics, and certain medical conditions, such as chronic renal failure.

Reference:
1. Kumar V, Abbas AK, Aster JC. Robbins Basic Pathology. 9th ed. Philadelphia, PA: Elsevier Saunders; 2013.