Mary Wilson was in elementary school when she signed up for a talent show. Florence Ballard was there, too. Although they lived in the same neighborhood, the two did not know each other. But Wilson was impressed with Ballard’s powerful voice. They became friends, and promised each other that if singing opportunities came up, they would contact each other. And boy, did an opportunity arrive. On a playground, Ballard met someone who wanted to put a “girl group” together to sing with The Primes. It was called the Primettes. The group later …