A US employee who works in Saudi Arabia most likely works in

A. Revenue and Taxation.

B. Planning.

C. National Security and Foreign Service.

D. Governance.

The correct answer should be C. National Security and Foreign Service.

Revenue and Taxation, Planning, and Governance, are most commonly consisting of jobs that are about internal affairs, that is, something done in the United States or its territories. Foreign service is done in foreign countries so if the person works in Saudi Arabia, for example in an embassy, then it's in the domain of foreign services.