What type of airspace is classified as Class B?

Class B airspace is designed to manage air traffic around major airports where significant levels of traffic exist. It is characterized by its structure, which typically extends from the surface up to 10,000 feet above sea level, creating a three-dimensional area shaped like an upside-down wedding cake. The stringent operational requirements within Class B airspace include the necessity for pilots to obtain air traffic control (ATC) clearance before entering. This is crucial for maintaining safe separation between the high volume of arriving and departing commercial airliners and general aviation traffic. The presence of ATC provides oversight and ensures that pilots operate safely within this busy airspace.

The other options describe airspace characteristics that do not align with the defined features of Class B. Airspace around small regional airports would typically be Class D or Class E. Moreover, describing airspace with no controlled traffic applies to uncontrolled airspace like Class G, while airspace designated specifically for training flights does not fit into any particular classification. Hence, Class B's requirement for ATC clearance and its association with major airport operations distinctly define it from other types of airspace.