Final answer:
The Roman Catholic Church's Doctrine of Papal Infallibility is a major obstacle to reconciliation with Protestant groups, as it claims the pope cannot err in matters of faith or morals. This doctrine, defined long after the initial Protestant Reformation, contrasts with Protestant views on human fallibility.
The correct option is A.
Step-by-step explanation:
A major stumbling block to reconciliation with Protestant groups is the Roman Catholic Church's Doctrine of Papal Infallibility.
This doctrine, not formally defined until the First Vatican Council of 1868, asserts that the pope is incapable of error when proclaiming a doctrine of faith or morals. It is a significant point of divergence between Catholicism and Protestant denominations, which do not accept the infallibility of any human, including the pope.
To understand the historical context, the Protestant Reformation was characterized by challenges to various Catholic doctrines and practices. Martin Luther's protest, documented in the Ninety-five Theses, objecting to the sale of indulgences, is an example of the criticisms that gave rise to Protestantism.
The Council of Trent was a response by the Catholic Church to address these challenges and initiate much-needed reforms, although it did not reconcile differences concerning the papal authority or indulgences.
The correct option is A.