Under US Tax Law, What Happens to Excess Foreign Tax Credit

Under U.S. tax law, what happens to excess foreign tax credit?

A) It reduces taxes on ordinary income in the current year.
B) It can be carried back one year to calculate a refund on additional taxes paid in U.S. on foreign source income.
C) It is lost unless the average foreign tax rate paid by the company in the future is greater than the U.S. tax rate.
D) None of the above