Which of the following is a hermaphrodite animal?

A. Elephant

B. Cow

C. Dog

D. Earthworm

Option A - Elephant

Elephants are dimorphic mammals, meaning there is a significant size difference between males and females. Male elephants can be twice the size of females. Secondary sexual characteristics, such as tusk and skull size, also show dimorphism between the sexes.

Option B - Cow

A cow refers to a female that gives birth to a calf, while a bull is a male that can breed. Male and female reproductive organs are separate, so a cow is not a hermaphrodite.

Option C - Dog

A dog is a domesticated carnivore belonging to the Canidae family. It is not a hermaphrodite because male and female sex organs are distinct. A female dog is referred to as a bitch.

Option D - Earthworm

Earthworms are hermaphrodites, meaning they possess both male and female sex organs. Each earthworm produces both sperm and eggs, but despite being hermaphrodites, they still require a mate to reproduce.

Thus, the correct answer is Option (D).