According to U.S. regulations, when a tank vessel is discharging cargo, each sea suction valve connected to the vessel's oil transfer, ballast, or cargo tank systems must be which of the following?

Correct Answer: Option A — sealed or lashed closed

Under 33 CFR 155.820, all sea suction valves connected to cargo or transfer systems must be securely sealed or lashed closed during cargo discharge operations to prevent accidental outflow of oil or intake of untreated ballast.