Question

Definition of species is --

Species is a natural group of organisms
All members of a species are identical in morphology
Members of a species can interbreed among themselves
Members of a species can not breed with members of another species

Answer 1

Biological species concept: Species are group of actually or potentially interbreeding natural populations that are reproductively isolated from other such groups (Mayr 1942)
Although appearance is helpful in identifying species, it does not define species
The interspecific hybrids are sterile
The most suitable answer is C