Looking at the answer options:

'pressurisation' --> INCORRECT. Not all cargo holds are pressurised. Or, does the examiner mean the aircraft's pressurisation system, in which case no one is going to breath.

'air recycling of the cargo compartment' --> CORRECT. See below for more information.

'trim air' --> INCORRECT. Maybe on a submarine, not so much in an aircraft.

'total air-conditioning' --> INCORRECT. Shutting down the TOTAL air-conditioning means no-one on board is breathing.

CARGO COMPARTMENT FIRE

When smoke is detected in a cargo compartment, visual and aural warning indications are provided at the flight deck, which also has controls for the cargo compartment fire suppression system. The first step in controlling and suppressing a fire (after turning off the aural warning) is shutting down the airflow to the cargo compartment. All ventilated cargo compartments have a means for shutting off the airflow from the flight deck. Following airflow shutdown, fire extinguishers must be discharged.