To drive on Taxiway C, what is required?

Driving on Taxiway C at O'Hare Airport requires specific operational protocols to ensure safety and efficient communication with air traffic control. The correct choice highlights the necessity of having an operational transponder, which is a device that helps identify and track vehicles and aircraft in the airspace, along with the use of the appropriate frequency, which in this case is 128.15. This frequency is specifically designated for communication with the control tower, facilitating essential dialogue regarding the vehicle's movements on the taxiway.

Utilizing the correct frequency is critical to avoid potential conflicts or misunderstandings with air traffic control, as each frequency serves a specific purpose and is monitored by different entities within the airport's air traffic management systems. Ensuring both an operational transponder and the correct frequency helps maintain coordination and safety in a busy airport environment, safeguarding not only ground operations but also the aircraft in transit.

The other options suggest alternative frequencies or requirements that do not align with the established communication protocols for accessing Taxiway C, which is why they do not meet the requirements needed for safe operation on that particular taxiway.