The key characteristic features of all the mammals are the mammary gland, skin with hairs, seven cervical vertebrae, 12 pairs of cranial nerves and muscular diaphragm. As giraffe, camel, bat and whale are the mammal and thus possess seven cervical vertebrae. Four chambered heart is present in all the mammals, birds and some reptiles like a crocodile. Enuceated RBC is the characteristic feature of all the mammal except camel. WBCs are always nucleated. Thus, the correct answer is option C.