Nwhich way did military and economic problems interact in the decline of the byzantine empire?

Military and economic problems have always been strongly intertwined and this wasn't any different in the times of the Byzantine Empire where vast expanses of land had to be readily monitored and guarded. This was obviously a severe financial undertaking which had to be funded. Dee to lack of money with time, the borders weren't as defended as they were in the past. 

Ithink the answer is d.