JAMB Biology 1982 Question 24

In man identical twins occur when

1. A.an ovum is fertilized by a sperm and then divides into two each forming a separate embryo
2. B.an ovum is fertilized by two sperms and then divides into two, each forming an embryo
3. C.two ova are fertilized at the same time each forming an embryo
4. D.two ova are fertilized by a single sperm each forming an embryo after fertilization
5. E.one ovum first divides into two and each half is fertilized by a sperm before developing into an embryo.