Rather than have a global economy in which each country specializes entirely in what it produces most efficiently, most countries produce goods that they also import. (For example, the United States both produces and imports automobiles.) This can best be explained by the fact that:a. Most countries use tariffs and quotas to restrict imports.b. Most consumers prefer to buy imported goods.c. Market economies cannot trade efficiently with non-market economies.d. As countries move toward specialization, opportunity costs change rather than remain constant.