Final answer:
In some ruling classes and cultures, brother-sister unions are an exception to the generally accepted incest taboo as part of the practice of endogamy, which is the marriage within a specific group for maintaining lineage or power. Therefore correct option is B
Step-by-step explanation:
In the context of marriage within ruling classes such as those of the Incas, ancient Egypt, ancient China, and some Hawaiian cultures, the practice of marrying within a specific social group, including close kin such as brother-sister unions, is known as endogamy. Endogamy is the cultural practice of marrying within a specific group to which one belongs, whereas marrying outside one's group is referred to as exogamy.
The incest taboo, which prohibits sexual relationships between close kin, is widely accepted across societies, but there are notable exceptions where certain royalty or ruling classes have practiced endogamous unions, often for reasons of maintaining purity of lineage, consolidating power, or adhering to religious or cultural beliefs.