• All processes are both internally as well as externally reversible.
• BIntake and exhaust processes are constant volume heat rejection processes.
• CThe combustion process is a constant volume heat addition process.
• DThe working fluid is an ideal gas with constant specific heats.

Air-standard cycles are assumed internally reversible (each process is quasi-static/frictionless), but external reversibility (matching temperature with the surroundings during heat transfer) is NOT required or assumed — the heat addition/rejection processes are simply modelled as constant-volume processes with an external source/sink at any temperature. So option A overstates the assumption; B, C, D are all standard air-standard Otto cycle assumptions.