Secretary of the Treasury, Secretary of Defense, Attorney General
Out of those three that is what the answer would be. But if you were to need the whole line it would be:
1. Vice President 2. Speaker of the House of Representatives 3. President Pro Tempore of the Senate 4. Secretary of State 5. Secretary of the Treasury 6. Secretary of Defense 7. Attorney General 8. Secretary of the Interior 9. Secretary of Agriculture 10. Secretary of Commerce 11. Secretary of Labor 12. Secretary of Health and Human Services 13. Secretary of Housing and Urban Development 14. Secretary of Transportation 15. Secretary of Energy 16. Secretary of Education 17. Secretary of Veterans Affairs 18. Secretary of Homeland Security
