Which classes of controlled airspace exist in the UK?

The correct classification of controlled airspace in the UK includes Class A, C, D, and E.

Class A airspace is utilized primarily for high-altitude traffic where air traffic control provides separation between all aircraft, primarily covering cruising levels. Class C airspace is used around major airports and is where both IFR (Instrument Flight Rules) and VFR (Visual Flight Rules) flights can operate, with ATC providing separation between IFR flights but not necessarily for VFR flights. Class D airspace is generally found around airports where there is a control tower, and provides a controlled environment for aircraft coming in and out, with ATC services being available to all pilots. Lastly, Class E airspace is less restrictive and can be used for IFR operations as well as some VFR traffic; it operates with differing levels of separation depending on the airport.

In contrast, the other answer choices include classes that are not defined or utilized in the UK airspace structure, such as Class B and G. Class B is primarily used in the US system and does not exist in the UK. Class G represents uncontrolled airspace and is not categorized as managed airspace that requires ATC interaction, hence it should not be included in the answer.