D. By reading the hot temperature gauges on the washing machine and the water heater
Explanation:
If they are using a machine for washing the utensils then there is no place to insert a thermometer into running tap water. Everything is done in the machine.
There is no need to run a separate instrument through the machine since the machine itself has instruments to measure the temperature of the water.
Using a surface probe would not be accurate enough since the utensils would considerably cool off by the time they exit
