Why can whales not breathe underwater?

Whales and dolphins are mammals and breathe air into their lungs, just like we do. They cannot breathe underwater like fish can as they do not have gills. ... After each breath, the blowhole is sealed tightly by strong muscles that surround it, so that water cannot get into the whale or dolphin's lungs.

x would be the most and the least would be y because there are more fruit   and seeds than flock z has insects