c. result from two eggs fertilized by different sperm.
Identical twins as a matter of fact. Identical twins are also called monozygotic babies. They came from one independent egg cell which was fertilized and then develops to become into two separate embryos. In the cases which can specifically involve interaction between these two embryos is monoamniotic twins which share the same amniotic sac and conjoined twins which can cause direct contact from their bodies.
