Final answer:
The combining form 'pyel(o)' is related to the C. renal pelvis, a structure within the kidney that collects urine before it passes into the ureter.
Step-by-step explanation:
The combining form pyel(o) is related to the renal pelvis.
The renal pelvis is a funnel-shaped structure within the kidney to which the calyces join, and it narrows down to become the ureter.
It is responsible for collecting urine before it passes into the ureter and is transported to the urinary bladder. Therefore, the correct answer to the question is C. renal pelvis.