Under Annex I, discharges are permitted only when the following conditions are met: ship en route, discharge filtered, oil content not exceeding 15 ppm.

• A. The ship is en route, the discharge has been filtered through oil filtering equipment, and the oil content does not exceed 15 ppm.
• B. The ship is in port, and the discharge is filtered.
• C. The ship is at anchor, and the oil content does not exceed 15 ppm.
• D. The ship is en route, but no filtration is required.

Answer: (A)

Under Annex I, discharges are permitted only if three conditions are met: the ship is en route, the discharge has passed through oil filtering equipment, and the oil content is 15 ppm or less. Being en route means discharges are not allowed in port or near land; the discharge must be treated at sea. Filtering is essential because it reduces the oil content before release, and the 15 ppm limit is the maximum allowed concentration of oil in the discharged water. Together, these rules protect the marine environment by ensuring treated bilge water is as clean as practicable before being discharged. The other options fail because discharging in port or at anchor isn’t allowed under these terms, and discharging without filtration would not meet the required oil content limit.