Arrange the following in order from lowest to highest level of economic integration.
A) customs union→economic union→free trade area→common market
B) economic union→customs union→common market→free trade area
C) common market→free trade area→economic union→customs union
D) free trade area→customs union→common market→economic union
E) common market→economic union→customs union→free trade area
Answer: D) free trade area→customs union→common market→economic union