What is it like to be an exact copy of another human being? 48 Hours examines this fascinating question, exploring the lives of twins as well as quadruplets. 48 Hours' "Multiple Choice" introduces you to some twins who for more than 40 years didn't even know each other. You'll also meet a woman who was determined to bear her quadruplets, even if it endangered her own life. And you'll learn the truth about Correspondent Erin Moriarty and her twin sister Sheela. Identical or fraternal twins? Find out. When Cathy Cimoch found out she was pregnant with quadruplets, she decided she'd try to have all four. But the difficulties prove tremendous. Will her babies survive? Many identical twins - even those raised separately - are remarkably alike, down to their hairstyles. But others are drastically different. What determines these outcomes? Is it genes, or environment? For more than 40 years, Erin Moriarty and her sister thought they were identical twins. But are they? Or was the doctor who delivered them mistaken?