Option C is correct option.

Pigeons belong to the class Aves because they possess key characteristics that define this group, including feathers, hollow bones, and being warm-blooded. They lay hard-shelled eggs and have a beak without teeth, which is adapted to their diet. These features differentiate pigeons from other classes, such as Mammalia and Reptilia, which have distinct adaptations like fur, live birth (in most mammals), or scales.

Hence, other options are incorrect.