The statement that best describes the Incan social class structure is: Lower ranking nobility held government positions.
Incan society had a well-defined class system with nobility at the top, and many lower-ranking nobles held important government roles and responsibilities. While some nobles were indeed related to the Sapa Inca (the emperor), it was not a strict requirement for all nobility. Not all Incans were nobles, and the majority of the population were common people, including farmers and laborers.