Which of the following best describes Spain under Isabella and Ferdinand? A tolerant of different religions B culturally diverse C free from internal struggles

I believe it to be choice C.

Under Ferdinand and Isabella, the Moorish Muslims that once ruled Spain were driven out, making Spain a Catholic nation and European power. The Reconquista was for the native Spaniards to take back Spain under Christian rule, meaning not too tolerant of different religions (ignoring choice A).

This also leads to a lack of cultural diversity, even though Spain at the time was at one time a connection of Spanish kingdoms. However, under Isabella and Ferdinand, the kingdoms of Aragon and Castille overthrew the lesser kingdoms that border Spain, thus limiting diversity - for there were Aragonians and Castilians. Also, Jews (and other non-Catholics) were persecuted, so ignoring choice B.

Despite the persecution of non-Catholics and wars that made Spain a massive, thriving power in Europe, Isabella and Ferdinand led the kingdom to prosperity. With the Armada and Christopher Columbus' discovery of America, Spain was the first nation to seek worldly power.