Explanation: An open secondary winding in a coupling transformer breaks the signal path to the next stage, resulting in no signal. **A) Replacing the transformer:** This is a straightforward and effective repair. It restores the circuit to its original design and function by installing a working component in place of the faulty one, ensuring proper signal transfer and impedance matching. **B) Changing to impedance coupling:** This is an alternative, valid repair if a replacement transformer isn't available or if circuit modification is desired. Impedance coupling uses a plate load resistor or choke, a DC blocking coupling capacitor, and a grid resistor to transfer the AC signal between stages while maintaining proper DC bias. This method effectively achieves the same goal of passing the audio signal from the output of one stage to the input of the next. Since both methods are satisfactory ways to restore the signal path and functionality, C, encompassing both A and B, is the most comprehensive correct answer.