The correct option is D All of the above
Explanation: Preferential Trade Agreements (PTAs) have been proliferating, especially since the establishment of the World Trade Organisation (WTO) in 1994. As of 1st December 2015, the WTO had received notifications of no less than 619 PTAs (disaggregated by goods, services, or accessions), of which 413 were already in force.
A free trade area is basically a preferential trade area with increased depth and scope of tariffs reduction. All free trade areas, customs unions, common markets, economic unions, customs and monetary unions and economic and monetary unions are considered advanced forms of a PTA.