The correct answer is D) "To be a member of the nobility, you must be related to the king."
In order to be part of the nobility, it is requisite that the individual is related to the Incan King.
Whenever the Incas extended their territories, they presented themselves to the rulers of these new lands and informed them that from now on, they will be ruled by the Incan Empire. A refusal from them will result in military affairs.
After overtaking the land, local rulers who initially refused to grant the lands to the Incan King were executed. Their siblings were taken to Cuzco and indoctrinated into Inca administration systems. They would then be allowed to return to their lands to become local rulers, and as such, become nobility, In some cases, they were allowed to marry daughters from the nobility.