The correct option is
D Turtle
Turtles belong to Phylum Chordata of the Reptilia class. Turtles are reptiles since they are four-legged vertebrates in addition to having cold-blooded metabolism and having scales covering their bodies. Breathing is aided by their lungs like in all other reptiles like the crocodiles, Snakes, lizards and the Tuatara.
So, option D is the correct answer.