21. What is the fog signal for a power driven vessel of 150 meters in length when at anchor inrestricted visibility?
(A) Sound the bell for about 10 seconds in the fore part and after the ringing of the bell the gongshall be sounded rapidly for about 10 seconds in the after part of the vessel every two minutes.
(B) Sound the bell for about 5 seconds in the fore part and after the ringing of the bell the gongshall be sounded rapidly for about 5 seconds in the after part of the vessel every two minutes.
(C) Sound the bell for about 10 seconds in the fore part and after the ringing of the bell the gongshall be sounded rapidly for about 10 seconds in the after part of the vessel every minute.
(D) Sound the bell for about 5 seconds in the fore part and after the ringing of the bell the gongshall be sounded rapidly for about 5 seconds in the after part of the vessel every minute.