Concept:The Hausa Bakwai are the seven major independent Hausa city-states.
Kebbi is not among them.
Explanation:The recognised Hausa city-states are Biram, Daura, Gobir, Kano, Katsina, Rano, and Zaria.
Kano, Daura, and Katsina all belong to this group.
Kebbi belongs to the Banza Bakwai group, not the core independent Hausa city-states.
So Kebbi is the exception among the options.
Answer:D. Kebbi