Consider A Combustion Efficiency Test is a measured metric determined by a Service Technician using a Combustion Meter when servicing a Fossil Fuel Consuming Appliance. Which of the following statements is/are True? Select one: a. It is only possible to do this test with Gas-Fired Furnaces. b. It is the concentration of Carbon Monoxide in the Combustion Gas that is what the Test measures and is the defining parameter as to whether the appliance is operating within designed performance. c. It is only possible to do this test with Oil-Fired Boilers. d. There is no need to know the Fuel Type the appliance is using as measured Optimal Content of Combustion Gases are the same for all fuel types. e. This test is not applicable to Heat Pumps of any Type