Which of the following is NOT a cabinet department?

The Department of Civil Affairs is not a cabinet department, which makes it the correct answer to the question. In the U.S. government, cabinet departments are the principal units of the executive branch, headed by a Secretary who is a member of the President's cabinet. The departments listed in the other choices, such as the Department of Transportation, the Department of Agriculture, and the Department of Defense, are all recognized cabinet departments. Each of these serves specific roles in federal governance, focusing on areas like national defense, agricultural policy, and transportation infrastructure.

Civil Affairs, in contrast, is not an established cabinet department. While there are various federal entities and offices focusing on civil affairs – particularly in contexts of military operations and community engagement – it does not hold the same statutory cabinet-level status as the other departments listed. This distinction is crucial in understanding the structure and organization of the federal bureaucracy.