When filter leak testing cannot be conducted by probe-scanning the downstream surface of the filter, itis necessary toa. make a measurement by inserting the probe 10 duct diameters downstream of the filter and using the average of10 readings taken at pitot traverse locations along one duct diameter.b. make a measurement by inserting the probe in the center of the duct at a downstream location 1 duct diameterfrom the filter.c. make a measurement by inserting the probe in the center of the exhaust duct and 1 inch above the downstreamface filter.d. make a measurement by inserting the probe into the duct at a downstream location that will produce a well-mixedaerosol.e. omit the filter