More Europeans were literate because of several things:
Witchcraft was not a common activity for women in the late Middle Ages.
Spain's rulers backing the Inquisition
The Inquisition was a group if institutions within the government system of the Catholic Church, whose aim was to combat heresy. It started in 12th century France and spread to other European countries resulting in the Spanish and Portuguese Inquisitions. Minor religions were more numerous in these countries
An Internet search of the question found a possible answer could be that once the plague ended, it never returned to Europe.
Without seeing the multiple choices that were offered in the test, you could answer with almost anything.
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C. Respect for the Mongols