How did the Allies leverage their geographical position after the Axis powers surrendered to them in Tunisia?

Allies used their position in Tunisia to launch an attack and end the African front.

Explanation:

The location of Tunisia on the coast meant that it can serve as a strategic base to receive more troops and other amenities and launch a  full blown assault on the Axis positions inside Africa.

From there they were able to bridge the gap between the Iberian region going up which was vital for them to win the war

Thus Tunisia had proven to be a smart victory in terms of strategy as it led to a lot many other attacks that were headed from the regions and improved the allied positions.

b). (sounds as the best answer)