Final answer:
Dizygotic twins result from the fertilization of two separate ova by two separate sperm, so the nurse would base the explanation on option 1) Two ova fertilized by separate sperm.
Step-by-step explanation:
Dizygotic (fraternal) twins result from the fertilization of two separate ova by two separate sperm. Each zygote develops independently, so dizygotic twins are not genetically identical. Therefore, option 1) Two ova fertilized by separate sperm is the basis for explaining dizygotic twins to a couple.
When describing dizygotic twins to a couple, the nurse would base the explanation on the fact that they are the result of two ova fertilized by separate sperm. Dizygotic or fraternal twins are genetically similar to siblings born at different times because they develop from separately fertilized eggs, each with a unique combination of genetic material from each parent.