The hippopotamus population has declined over the years. climate change and human predators have caused their numbers to decline. what adaptation could prevent their future extinction? a) they only give birth to one calf every other year. b) their large size makes them difficult to approach from a predators stance. c) their feet have membranes between their toes making it easy to move in water. d) their body is almost completely hairless except for a few bristles around their mouths.