The correct answer is C. Constant strife created the need for protective architectural elements in the construction of buildings.
Indeed, the Paston letters were written during a very troubled and deadly period in English history, when not only its population was being ravaged by the Black Death but the War of the Roses had divided the population and the resulting civil war and spread lawlessness were very imminent dangers and concrete threats to life and property. Since violence was prevalent, any type of housing needed to be fortified since the possibility of an attack was very present, especially considering that the Pastons were in one of the belligerent camps.