Explanation: Commercial radio operators on duty and in charge of a transmitting system must have their original license or a photocopy readily available for inspection by the FCC. This is a fundamental regulatory requirement to verify the operator's qualifications. It ensures that only properly licensed individuals are operating commercial radio equipment. The license can either be posted at the control point or kept in the operator's personal possession. A) A Proof-of-Passing Certificate (PPC) is a temporary document received after passing an exam; the actual license is required for on-duty operation. C) FCC Form 756 is an application form for a license, not the license itself, and is not required to be on hand by the operator. D) While an employer might request a copy, it is not an FCC regulatory requirement for the operator to supply it to a supervisor as the primary means of compliance for FCC inspection.