The correct answer is A) occluded cyclone or occluded front. In the final stage of a cyclone's development, the warm and cold fronts associated with the cyclone merge, creating an occluded front. This occluded front marks the transition of the cyclone from an active, developing stage to a mature, dissipating stage, which is known as an occluded cyclone. The other options are incorrect because: B) polar cyclone refers to a large-scale, long-lived weather system in polar regions, not the final stage of a cyclone; C) anticyclone is the opposite of a cyclone, with high pressure at the center; and D) tornado is a violently rotating column of air, not the final stage of a cyclone's development.