With respect to the excretory system of Rana tigrina, which statement correctly identifies its structural units and primary nitrogenous waste?

Malpighian tubules; uricotelic animal eliminating insoluble uric acid crystals.
Flame cells; ammonotelic animal releasing free toxic ammonia gas directly into air.
Uriniferous tubules or nephrons; ureotelic animal excreting urea separated by the kidneys.
Solenocytes; ureotelic animal synthesizing urea directly within the lumen of the urinary bladder.

Correct answer · Option 3

Uriniferous tubules or nephrons; ureotelic animal excreting urea separated by the kidneys.

Each kidney is composed of uriniferous tubules or nephrons. The frog excretes urea and is therefore a ureotelic animal.