Which department is responsible for assisting and debriefing the president on all foreign matters?
a. department of defense
b. department of the interior
c. department of state
d. department of homeland security

Department of Foreign Affairs is usually responsible for most of the foreign matters, but the a. Department of Defense also debriefs the president on foreign matters that can escalate, because of the FAA act of 1961.

Ibelieve the answer is the  third option, or c.