Descent groups are:​

A) ​based on residence rules
B) ​strict clan memberships
C) various nonkin institutions
D) ​based on a common ancestor

Descent groups are based on a common ancestor, tracing lineage through either the paternal or maternal line. They are important for determining kinship ties, inheritance, and social standing in many societies. Residence rules and clan memberships may be associated with descent groups, but are not defining characteristics. Nonkin institutions are not considered descent groups.