Hong kong, south korea, taiwan, and singapore are sometime referred to as the "four " because of their rapid industrial economic growth.

Hong Kong, South Korea, Taiwan and Singapore are called as Four Asian Tigers.

Explanation:

The four countries Hong Kong, South Korea, Taiwan and Singapore were in the zone of developing countries before 1980s. All of them moved to the newly industrialized countries with their rapidly growing economies. They have enormously gained influence in trade and development, well developed infrastructure, excellent export logistics. This made them ideal in expanding into East Asia. These economies have proved their excellent resilience in withstanding the crises of 1997 (Asian financial) and 2008 (global financial). International Monetary Fund (IMF) has included these countries under its most advanced economies.  

A,) cause a & b are equal & both gives 180°

The answer to the question is c.