The european union has positively affected the economies of europe by a) refusing to allow countries to trade with each other. b) allowing england to become the richest european country. c) lowering or eliminating barriers that slow down trade between countries. d) making taxes on imported goods higher and promoting economic independence.

C) lowering or eliminating barriers that slow down trade between countries.

The European Union (EU) is a political and economic group of 28 European countries. One of its most important achievements has been the introduction of a single market through standardized laws and a common currency (although not all countries in the political union belong to the monetary union). It has also tried to eliminate barriers to the movement of people, goods and services.

i think it is the third one.

the factors that the economies of the muslim empires prosper were:

1- land trade routes-located between three continents  

2- sea trade routes

trade contributed to the spread of muslim empires, and with that islamic culture led to a growing feeling of internationalism resulted in the transfer of technology, science, and other cultural forms.