Final answer:
The Department of Homeland Security serves as the primary contact for supporting agencies assisting at an incident in the United States.
Step-by-step explanation:
The subject of this question is Social Studies and the grade level is High School.
The primary contact for supporting agencies assisting at an incident is the Department of Homeland Security. They are responsible for overseeing agencies charged with protecting the territory of the United States from natural and human threats.
For example, during a natural disaster such as a hurricane or earthquake, the Federal Emergency Management Agency (FEMA) is the primary contact for supporting agencies. They coordinate the response efforts and provide resources and assistance to affected areas.