In the pressure-volume diagram, shown in the illustration, what is indicated to have occurred by the line connecting points 'd' and 'e'? Illustration MO-0035

Correct Answer: Option A — The combustion gases have expanded.

The downward slope connecting points d and e on the pressure-volume diagram represents the power expansion stroke, where high-pressure combustion gases expand against the retreating piston. During this phase, thermal energy is successfully converted into mechanical work.