单项选择题
A.turn it off for five minutes every half-hour
B.turn it off and on at five-minute intervals
C.turn it off during daylight hours
D.leave it on continuously
单项选择题 A tug is approaching a broken down steamer in moderately heavy weather preparing to take it in tow. In most cases the（）.
单项选择题 A tourniquet should be used to control bleeding ONLY（）.
单项选择题 A survival craft being used to pick up a person who has fallen overboard from a vessel should approach the person（）.