What late 15th-century development set the stage for Spain being newly

What late 15th-century development set the stage for Spain being newly able to launch expeditions of discovery in the Atlantic?

A) the fall of King Ferdinand and Queen Isabella of Spain from power
B) the expulsion of all Jews from Spain
C) the division of Spain into four Christian kingdoms and one Muslim kingdom
D) the political, religious, and cultural unification of Spain led by King Ferdinand and Queen Isabella of Spain, culminating in 1492 with the Reconquista

ANSWER
Answer: D