Answer:
B. Customs union
Explanation:
Custom Union is a trade relationship agreed on by two or more countries in which they decided to remove barriers to free trade, such as removing heavy cost duties, high tariffs, between agreeing nations. It is considered a form of economic Integration.
The main aim of custom unions is to allow free trade between member Sates. It also helps to reduce administrative bottle neck and financial burdens which could be barriers to trading.