Consider the following statements:

A. A group can have zero elements.

B. A group cannot have any element which is idempotent except the identity element.

C. An isomorphism from a group $\langle G,\rangle$ to $\langle G,\rangle$ is called an automorphism.

D. If every element in a group is its own inverse, then the group must be abelian.

Choose the correct answer about the four statements given above.