why? read this from wikipedia.org and it will explain it to you.
the treaty of tordesillas (portuguese: tratado de tordesilhas [tɾɐˈtaðu ðɨ tuɾðeˈziʎɐʃ], spanish: tratado de tordesillas [tɾaˈtaðo ðe toɾðeˈsiʎas]), signed at tordesillas on june 7, 1494, and authenticated at setúbal, portugal, divided the newly discovered lands outside europe between the portuguese empire and the crown of castile, along a meridian 370 leagues[note 1] west of the cape verde islands, off the west coast of africa. this line of demarcation was about halfway between the cape verde islands (already portuguese) and the islands entered by christopher columbus on his first voyage (claimed for castile and león), named in the treaty as cipangu and antilia (cuba and hispaniola).
the lands to the east would belong to portugal and the lands to the west to castile. the treaty was signed by spain, 2 july 1494, and by portugal, 5 september 1494. the other side of the world was divided a few decades later by the treaty of zaragoza, signed on 22 april 1529, which specified the antimeridian to the line of demarcation specified in the treaty of tordesillas. originals of both treaties are kept at the general archive of the indies in spain and at the torre do tombo national archive in portugal.
this treaty would be observed fairly well by spain and portugal, despite considerable ignorance as to the geography of the new world; however, it omitted all of the other european powers. those countries generally ignored the treaty, particularly those that became protestant after the protestant reformation.
that would be the sahara desert.
the answer is d.clouds are formed through evaporation and then condensation.