I believe the answer is: A. Peasants had an opportunity to move up in the social hierarchy by becoming artisans, merchants, or other types of professionals.
The formation of middle class during middle age started when the nobles and rich merchants started to act as patrons for other conventional profession at that time.
This allow jobs such as artisans, bards, actors, designers comedians, and scientist to obtain a higher income by providing their services to the rich patrons.