The correct option is C Nephrostomes
From the necks of the Malphigian bodies, short solid rods of cells grow towards the peritoneal epithelium and fuse with it. These rods soon become hollow and open into the body cavity by ciliated funnel-shaped mouths called nephrostomes. The nephrostomes in the adult frog are as many as 200 or more and are present on the ventral surface of the kidney and are minute funnel-like ciliated openings, leading by short tubes into the renal veins.
So, the correct answer is option B.