The purpose of a flow switch installed in a hot water supply line to an air-handling unit is to
a. Stop the fan and close the outside air dampers if the low limit temperature controller malfunctions or the heat source fails
b. Open the outside air dampers wide when the water flow is established
c. Open the hot water supply valve further if the hot water flow drops below a safe limit
d. Close the outside air dampers and stop the fan if the flow of water is interrupted, to protect the coil from freezing
e. Alert the operator of a low flow condition
Answer: D