GM car sales dropped from 4 million per year in the mid-2000s, when the economy was in an expansion, to only 2.1 million per year at the end of the recession in 2009. The economy experienced a decade-long expansion beginning in 2009, and sales of GM cars and trucks climbed back to 3 million by 2015 and remained at about that level through 2018. Based on these changes in sales in response to changes in the country’s level of economic activity, are cars and trucks normal goods or inferior goods? Briefly explain. Assume that higher U.S. GDP results in higher incomes for most Americans.