Final answer:
The erroneous thought about the medieval period being marked by social equality is incorrect due to the existence of a rigid social hierarchy. While the Church had some positive impacts on life, it was not uniformly improved across the period, and opportunities for social mobility were limited but possible.
Step-by-step explanation:
The erroneous thought regarding the medieval period's lifestyle is C. The period was marked by social equality. This is not an accurate description of the time as there was a distinct social hierarchy with sharp divides between the classes. The feudal system and manorialism structured the society, where serfs and peasants were at the bottom, owing service and rent to the nobility. Life was not a mere struggle for survival nor was it simply unpleasant as the concept of 'bare survival' would suggest; many communities prospered, and there were moments of joy and cultural richness.
Despite the hardships, such as disease and lack of sanitation, which frequently led to early death, people of the medieval period experienced a variety of living conditions and could sometimes improve their status over generations. The Catholic Church did play a role in improving the quality of life through the preservation and dissemination of knowledge, as well as providing spiritual guidance. However, this role was complex and varied across regions and time periods.