Final answer:
The extended family is not one of the three most important subsystems according to Minuchin's structural family therapy model; spousal, parental, and sibling subsystems are the core components.
Step-by-step explanation:
The question is regarding Salvador Minuchin's structural family therapy model. In Minuchin's model, three subsystems are considered most important: the spousal subsystem, the parental subsystem, and the sibling subsystem. The extended family is not one of the three primary subsystems; although it can play a significant role in family dynamics, it is not a core focus within this specific model of family therapy.