Which of the following describes Class B airspace?

Class B airspace is specifically designed to manage air traffic in busy terminal areas around the nation's major airports. It is structured to provide a high level of safety and efficiency for both commercial and general aviation. This airspace requires pilots to obtain an Air Traffic Control (ATC) clearance before entering, ensuring that traffic is well-coordinated and minimizing the risk of collisions in busy airspace.

The distinction between Class B and other airspace classes, such as the other options presented, lies in its operational requirements and the environment it covers. For instance, military restrictions are not the defining characteristics of Class B airspace, nor is it associated with rural areas. Class B airspace is about managing high-density traffic, thus distinguishing it from areas without regulations or those that lack ATC involvement.