One Factor That Contributed to the Growth of Some Urban

One factor that contributed to the growth of some urban centers such as Paris and London was:

A) the growth of the universities associated with each city.
B) their ability to draw on the wealth of the immediate area around the city.
C) the development of an international trade zone surrounding each city.
D) their holding on to a larger population throughout the period of the dissolution of the Roman Empire.
E) their status as the capital of nation-states formed during the early medieval period.