Nephrons in birds, mammals, and reptiles are all extremely similar, more so than other structures in the bodies of different species, solidifying the relatedness through similarity.
Explanation:
Birds can be said to have "mammal-like" nephrons from the number of loops and overall structure of their kidneys, which, although they look very different, serve the same purpose and do it in largely the same way. Reptiles also have mammal-like nephrons, and it can be assumed that this evolutionary trait was kept because the specific structure of the nephrons is generally the most efficient.
I don't know the options but my best guess would be erosion. Every time water comes on the beach is takes sand which erodes the beach. Hope that helps!
