The development that most aided explorers in their ability to sail the oceans to discover the New World during the age of discovery was option D. More efficient ships.
Because of improvements that ships had in that age such as the stern-post rudder and lateen sails among others, greater maneuverability was offered to the explorers and ships had the chance to sail at any time of the year. Besides the building of bigger ships meant that smaller crews were required and the ships could sail longer distances without stopping; which was something really relevant for the explorers.