<span>In southern France, the Carcassonne gap is an ancient routeway leading from the Atlantic to the Mediterranean lands. Carcassonne is located southeast of Toulouse (about 90km) in the middle of the Massif Central and Pyrenees in France. It is situated in the intersection of the two main routes of traffic: the route that goes from the Massif Central to Spain and the route going from the Atlantic to the Mediterranean lands. </span>
"Planting trees throughout Sahel" is the one action among the following actions given in the question that would be the most effective long-term solution to fighting desertification in the Sahel.
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