A jack-up drilling unit elevated on the Outer Continental Shelf must have a fog horn that will sound（）.<br>A:a 2-second blast every 20 seconds<br>B:a 4-second blast every 20 seconds<br>C:an 8-second blast every 30 seconds<br>D:a 10-second blast every 30 seconds

A jack-up drilling unit elevated on the Outer Continental Shelf must have a fog horn that will sound（）.
A:a 2-second blast every 20 seconds
B:a 4-second blast every 20 seconds
C:an 8-second blast every 30 seconds
D:a 10-second blast every 30 seconds

出自：海船船员证

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