7. Which of the following statements is true?

a. The most important source of tax revenue for the federal government is individual income taxes.

b. The most important source of tax revenue for state and local governments is sales taxes.

c. The second most important source of revenue for state and local governments is local property taxes.

d. The taxation burden, measured by taxes as a percentage of GDP, is lighter in the United States than in most other advanced industrial countries.

e. All of the above are true.