The statement that is true about the spread of Catholicism is:
The Spanish Reconquista united the territories and religions of Spain, which allowed Spain to spread Catholicism more easily.
This is the most accurate statement as the Reconquista, which involved the conflict between Christians and Muslims in Spain, resulted in a unified Christian Spain which subsequently facilitated the spread of Catholicism, especially as Spain began its exploration and colonization efforts in the Americas. The other statements either contain inaccuracies regarding the relationships between Spain and Portugal or misrepresent historical events.