The correct answer is C) the operation of the watertight doors in cargo spaces must be recorded, as required by the SOLAS (Safety of Life at Sea) Convention. The SOLAS Convention specifies that the opening and closing of watertight doors in cargo spaces must be recorded, as this information is crucial for maintaining the overall integrity and safety of the vessel in the event of an emergency. This recording requirement ensures that the crew and authorities can monitor the status of the watertight doors and take appropriate actions if necessary. The other options are incorrect because SOLAS does not mandate that watertight doors in cargo spaces be of the sliding style only (A), be operated remotely from the bridge (B), or be fitted with a hand-operated mechanism (D). These are not the specific requirements outlined in the SOLAS regulations regarding watertight doors in cargo spaces.