What are the methods used by the United States to reduce the double taxation of income earned by foreign operations of U.S. companies? 

a. Exempting some foreign source income and allowing a deduction for all foreign taxes paid. 

b. Allowing a deduction for all foreign taxes paid and providing a foreign tax credit for foreign income taxes paid. 

c. Exempting some foreign source income and providing a foreign tax credit for foreign income taxes paid. 

d. Exempting some foreign source income, allowing a deduction for all foreign taxes paid, and providing a foreign tax credit for foreign income taxes paid.