If the governor fails to 'unload' the compressor, what would protect the reservoirs from becoming over-pressurized and bursting?

Answer: B — The safety valve

If the governor fails to 'unload' the compressor, manually turning off the compressor would not protect the reservoirs from becoming over-pressurized. Similarly, backup compressors may not always be readily available or functional. The relief valve, while important for regulating pressure, may not be able to handle a sudden, large increase in pressure. However, the safety valve, which is specifically designed to release excess pressure in cases of emergency, would provide the necessary protection for the reservoirs. Therefore, the safety valve is the best option for preventing over-pressurization and bursting in this scenario.