Which class of airspace includes all uncontrolled airspace?

The correct choice is that Class G airspace includes all uncontrolled airspace. Class G is defined as uncontrolled airspace, meaning that it is not actively monitored by air traffic control (ATC). Pilots operating in this airspace are responsible for their own navigation and separation from other aircraft.

Class G airspace can exist at various altitudes, typically starting from the surface up to the base of the controlled airspace, which may be at higher altitudes where controlled classes like Class E begin. This distinction is important because pilots need to be aware of the rules and conditions under which they fly in different airspace classes, especially when transitioning from uncontrolled to controlled airspace.

In contrast, Classes E, D, and C are all classified as controlled airspace, meaning they are subject to ATC regulations. Class E generally includes airspace that is controlled but has fewer restrictions than classes D and C, which are associated with airports and require more ATC oversight. Classes D and C airspace specifically surround busy airports where ATC is actively managing air traffic to ensure safe operations. Thus, Class G is the only class designated explicitly as uncontrolled, making it the correct answer for identifying which class includes all uncontrolled airspace.