Which of the following is a requirement for aircraft operating in Class C airspace?

In Class C airspace, aircraft are required to establish two-way radio communication with air traffic control before entering and while operating within that airspace. This requirement ensures safety by allowing for the effective management of air traffic, as the air traffic controllers can provide updates and instructions to pilots operating in a busy environment. This communication is crucial for maintaining situational awareness among all aircraft in the vicinity.

The other choices do not reflect the specific requirements for operations in Class C airspace. Daylight only operation is not a requirement for this airspace classification; aircraft can operate at any time, provided they maintain appropriate visibility and cloud clearance. Visual flight rules (VFR) are applicable to many types of airspace, but they are not a specific requirement for Class C, which can also accommodate instrument flight rules (IFR). Lastly, while filing a flight plan can be a good practice, it is not mandatory for all operations in Class C airspace.