Two-way radio communication must be established with which airspace facility before entry?

Establishing two-way radio communication is essential for safe operations in controlled airspace. In the case of Class C airspace, pilots are required to establish communication with the appropriate air traffic control facility before entering. Class C airspace generally surrounds airports with a significant number of commercial operations. This requirement ensures that air traffic controllers can manage the flow of aircraft in and out of busy areas effectively, enhancing safety and coordination.

In contrast, while Class D airspace also requires communication with the controlling authority, it is typically associated with smaller, regional airports, and the communication requirements are slightly less stringent than those for Class C airspace. Class B airspace entails more stringent requirements where pilots must receive ATC clearance prior to entry, while military airspace involves different regulations that do not specifically mandate radio communication with standard ATC facilities. Therefore, the crucial aspect of this question is that Class C airspace explicitly necessitates the establishment of two-way radio communication as a condition for entry, making it the correct option.