单项选择题
A.turn it off for 5 minutes every half-hour
B.turn it off and on at 5 minute intervals
C.turn it off during daylight hours
D.leave it on continuously
单项选择题 After an explosion，repair of emergency machinery and services should be accomplished（）.
单项选择题 A vessel sailing from Liverpool to New York puts into Boston，Mass. for emergency repairs. If no inward foreign cargo is to be discharged at that port，which of the following documents is required?（）
单项选择题 A vessel may enter a traffic separation zone（）.