Answer:
invansions by barbarian tribes
the most straightforward theory for the western rome collaspe pins the fall on a string of miltary
Light bulbs were the power source used in factories during the industrialization
I believe the answer is: C. development of medieval guild towns and cities
A long with urbanisation, the centre of all economic activities were started to shifted into large cities with highly populated area. When this happen, Guild towns that established to excel at a certain economic sectors would started to established in order to gather as much talented members as possible.