Final answer:
The increased size of cathedrals in the Romanesque and Gothic periods is mainly due to the need to accommodate pilgrimages to holy relics, with upgraded building technology and cultural changes also playing significant roles.
Step-by-step explanation:
The increased size of cathedrals during the Romanesque and Gothic periods can be attributed to several factors, including technological advancements and cultural shifts. The correct answer to the student's question is D: Cathedrals needed to accommodate the growing practice of pilgrimage to visit holy relics. As the trend of people moving away from the countryside and into towns and cities began, the intellectual life also shifted, leading to an increase in the prominence of cities like Paris and the constructing of grander cathedrals as symbols of civic pride. During the Gothic period, advances such as flying buttresses, pointed arches, and ribbed vaults allowed for the creation of larger and higher buildings with thinner walls and large windows. Furthermore, the strengthening of the French monarchy and centralized government, along with an increase in population and trade, brought people back to the cities, where the iconic Gothic cathedrals served both religious and socio-political functions.