automotive exam

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Oxides of nitrogen (NOx) contribute to the formation of A. photochemical smog. B. acid rain. C. particulate emissions. D. high levels of CO2. Technician A says that a converter that rattles when tapped with a mallet should be replaced. Technician B says that the root cause of a converter failure should be diagnosed and repaired before a replacement converter is installed. Who is correct?   Two technicians are explaining what exhaust gas emissions tell you about engine operation. Technician A says that the higher the level of CO2 in the exhaust stream, the more efficiently the engine is operating. Technician B says that CO2 levels of 20 to 25 percent are considered acceptable.   Technician A says that a 3 í— 5 card should be held against the oil fill opening if the positive crankcase ventilation (PCV) system is operating correctly. Technician B says that if a PCV valve rattles, it's working properly. Who is correct?  Oxygen combines with nitrogen in the air to form NOx at about _____