The answer is letter A.
Vietnam is not part of the Four Asian Tigers. Hong Kong, Singapore, South Korea, and Taiwan are known as the Four Little Tigers or Four Asian Dragons because of their highly free-market and developed economies. These four countries were successful in maintaining exceptionally high growth rates and rapid industrialization since the mid ‘50s to ‘90s. All four had already developed into advance and high income economies by the 21st century.
Hong Kong and Singapore are now world-leading international financial centers while South Korea and Taiwan are world leaders in manufacturing information technology. They currently serve as role models for developing countries like the Philippines.