Which classification method best shows how competitive a nation's economy is in global terms? a) Using phrases like "first world," "second world," and "third world." b) Classifying countries based on their level of development and using phrases like "more developed" or "less developed." c) Visiting each country and polling a select handful of the population about their income, etc. d) Calculating the GDP per capita of each country and using those numbers to create a global average that can be used as an economic yard stick.