I'll come clean. Here is one of the doubtful questions I am trying to analyse to see if we should ask for it to be pulled or not
As altitude increases, if the mixture is not leaned:
A the volume of air entering the carburettor remains constant and the fuel flow decreases
B the volume of air entering the carburettor decreases and the fuel flow decreases
C both the density of air entering the carburettor and the fuel flow decrease
D the volume of air entering the carburettor decreases and the fuel flow increases
One of those typical ATPL questions which merely serve to underline the lack of understanding of the questioner! The answer is system-specific, yet the system hasn't been specified. In terms of the most basic carburettor (in other words before system modifiers come into play), the volume of air increases due to the lower exhaust back pressure and the fuel flow decreases due to the lower pressure differential. Hence C is the only answer that's even vaguely correct.