Final answer:
Prince Henry the Navigator, the son of King John I of Portugal, is the Portuguese noble who began a navigation school in Sagres, aiding the Portuguese maritime discoveries. Pedro Cabral was the first explorer to reach Brazil and claim it for Portugal.
Step-by-step explanation:
The Portuguese noble who started a school for navigation was D) Prince Henry the Navigator. This initiative placed Portugal at the forefront of maritime exploration during the Age of Discovery. Prince Henry the Navigator, the third son of King John I of Portugal, established a navigation school in Sagres in 1416. This school brought together shipbuilders, cartographers, and instrument makers, significantly advancing Portuguese naval exploration, which led to the discovery of new sea routes and the expansion of Portuguese trade.
Regarding the first explorer to reach Brazil and claim it for the throne of Portugal, that distinction belongs to Pedro Cabral. Columbus, Magellan, and Cartier were prominent explorers of their time, but only Pedro Cabral is credited with the discovery of Brazil in 1500, thus expanding Portugal's holdings in the New World.