Which of the following statements concerning corporate income taxes is correct?

A. The federal income tax is applied at a flat rate across all levels of taxable income.

B. The marginal tax rate will always be higher than the average tax rate.

C. U.S. corporations are exempt from federal taxation.

D. The marginal tax rate will always be lower than the average tax rate.

E. Corporations pay 10% on their first $10,275 of income.