Mammals All mammals are warm-blooded and they feed their babies milk. Most mammals live on land, for example, humans and dogs. Some mammals, like whales, live in water, but they haven't got gills, They have all got ?__ Most of them have got hair and four legs.
lungs
Объяснение:
смотрите , gills это жабры(дыхательная система) , у китов нет жабр , есть легкие , тоесть lungs.