Which of the following class is being described by the given statements (i - iv)?
(i) They are found in a variety of habitats- polar ice-caps, deserts, mountains, forests, grasslands and dark caves.
(ii) Most unique mammalian characteristic is the presence of mammary glands by which the young ones are nourished.
(iii) Heart is four-chambered.
(iv) Sexes are separate and fertilization is internal.

A. Reptilia

B. Aves

C. Mammalia

D. Amphibia

Please do not use chat terms. Example: avoid using "grt" instead of "great".