Complementary goods are... A. Competing goods
B. Goods used together
C. Substituted for each other
D. Luxury goods​

Inspired by the example of that great cornellian, vladimir nabokov, some of your friends have become amateur lepidopterists (they study butterflies). often when they return from a trip with specimens of butterflies, it is very difficult for them to tell how many distinct species they've caught— to the fact that many species look very similar to one another. solution

As our current atmosphere formed, the concentrations of various atmospheric gases fluctuated. match each gas with the explanation that best describes how its proportion changed during the evolution of the atmosphere.

How does specialization enable countries to trade with one another? a country can make and sell goods affordably and buy goods that it is inefficient at making. a country can make what it chooses and sell its goods to other countries. a country can decide to buy everything it needs from other countries. a country can efficiently make goods that were once difficult to make.