When filling fuel-oil tank 4S on the DEEP DRILLER, it is necessary to open valve __________.

Correct Answer: Option C — 11

Valve 11 is the designated control valve for the fuel-oil transfer line leading to tank 4S on the DEEP DRILLER. Following the vessel's specific piping diagram is a critical safety requirement to ensure correct tank filling and to maintain the vessel's stability and trim during bunkering operations.