The textbook provides a lot of useful data about taxes and government spending in the United States over the past several decades. In general, what has been happening with taxes since the 1960s? a. Tax receipts have been falling consistently, from about 25% of GDP in 1960 to almost 7% today. b. Taxes have been rising consistently, from about 7% of GDP in 1960 to almost 25% today. c. Taxes have gone up and down on various occasions, but there is no general trend. Tax receipts as a share of GDP have stayed between 17% and 20% for many years. d. Tax receipts as a share of GDP have greatly declined as a result of widespread tax evasion