问题：

[单选] 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 nearest land