Economic Weakness of the Roman Empire Included All of the Following

Economic weakness of the Roman Empire included all of the following except

A) poor internal communications and transport.
B) the absence of a money economy.
C) nobles' failure to invest their wealth in commercial enterprises.
D) the lack of technological innovation, probably due, in part, to the availability of slaves.
E) the lack of productivity in the cities and the economic burdens cities placed on the countryside.