In man, identical twins occur when

• A.an ovum is fertilized by a sperm and then divides into two each forming a separate embryo
• B.an ovum is fertilized by two sperms and then divides into two each forming an embryo
• C.two ova are fertilized at the same time each forming an embryo
• D.two ova are fertilized by a single sperm each forming an embryo after fertilization