Final answer:
b) A 1st Class Grade A, B or C License. The shift engineer must have a 1st Class Grade A, B or C License to operate the hot water plant.
Step-by-step explanation:
To operate a hot water plant with a total boiler horsepower of 500 bhp and operating below 250 degrees Fahrenheit and 160 PSIG, the shift engineer must have a 1st Class Grade A, B or C License. This license ensures that the engineer has the necessary knowledge and skills to operate and maintain the hot water plant at the required level of competency.