A child presented with intermittent episodes of left sided flank pain.Ultrasonography reveals a large hydronephrosis with dilated renal pelvis and cortical thinning with a normal ureter. Kidney differential function was observed to be 19% which of the following is the best management:

• A. Pyeloplasty
• B. Nephrectomy
• C. Endopylostomy
• D. External Drainage