Answer:
A
Explanation:
Check the results obtained with a leaner setting of the mixture. In this case, engine roughness is probably caused by the mixture set being too rich for the high altitude. When the carburetor heat is turned on, the warmer air entering the carburetor is less dense, and tthis makes the mixture to be further enriched. The result of this phenomena is that the engine roughness increases. To solve this particular problem, it can usually be corrected by leaning the mixture.
