Answer:
D. Economic Union
Step-by-step explanation:
Economy's Integration can be of various levels : PTA, FTA, Custom Union, Common Market, Economic Union
Economic Union (particularly Monetary Union) sets following norms between countries - 1. tariff free goods & services trade, 2. uniform policies for external trade, 3. free labour & capital movement, 4. common fiscal policies, (monetary union - common currency, central bank).
Eg : European Union - Common Agricultural Policy (same fiscal policy) , same currency i.e Euro.
All others: Free Trade Area, Customs Union, Common Market are lesser integrative economic/ regional coopereation agreements. FTA includes only 1st feature of EU, Common Market & Custom Union also include only 1st , 2nd & 1st, 2nd, 3rd features respectively.