When a mother tells her older child not to interfere when she tries to discipline her younger child, the mother is defining the role of the:

A) ​sibling co-system.
B) ​parental subsystem.
C) ​family orientation.
D) ​societal role-player.

The mother is defining the parental subsystem, which is the subset of the family system that includes the parents and their unique relationship and roles in relation to the children. By telling the older child not to interfere in her disciplining of the younger child, the mother is asserting her role as the primary disciplinarian and caregiver in the family. The sibling co-system refers to the relationship and interactions between siblings, and is not relevant to this scenario. Family orientation and societal role-player are broader concepts that do not specifically relate to this situation.