Which metropolitan area is served by an airport with the code IAD?

Here is the question :

WHICH METROPOLITAN AREA IS SERVED BY AN AIRPORT WITH THE CODE IAD?

Here is the option for the question :

Washington, D.C.
Dallas, Texas
Boston, Massachusetts
Milwaukee, Wisconsin

The Answer:

And, the answer for the the question is :

Washington, D.C.

Explanation:

[STC0017851]. Formerly known as Dulles International Airport (DIA), it serves the Washington, D.C. metropolitan region. The letters were switched around to avoid confusion with DCA, the abbreviation for Washington National Airport (now known as Ronald Reagan International Airport). IAD has replaced Dulles.