Except as provided for otherwise，an oil tanker might discharge certain amount at certain rate of oil or oily mixtures into sea when ______.

A、the tanker is within 50 nautical miles from the nearest land
B、the tanker is no more than 50 nautical miles from the nearest land
C、the tanker is more than 50 nautical miles from the nearest land
D、the tanker is not more than 50 nautical miles from the