Ron Polonsky is a seventy-one-year-old retired distribution manager. He and his wife Sandra live in Lincoln, Nebraska. Sandra is fifty-seven and is employed as a high-school science teacher. She has family coverage through a group health insurance plan offered by the state of Nebraska. Ron is covered as a dependent on her plan. The Medicare Part B carrier for Nebraska is Blue Cross and Blue Shield of Kansas.

Which carrier is Ron's primary insurance carrier? Why?