Which of the following reflect comparative advantage, and which reflect macroeconomic forces?

a. Thanks to the development of huge oil sands in the province of Alberta, Canada has become an exporter of oil and an importer of manufactured goods.

b. Like many consumer goods, the Apple iPad is assembled in China, although many of the components are made in other countries.

c. Since 2002, Germany has been running huge trade surpluses, exporting much more than it imports.

d. The United States, which had roughly balanced trade in the early 1990s, began running large trade deficits later in the decade, as the technology boom took off.