After reporting a casualty to a mobile offshore drilling unit，which record must be retained on board? （） ["Record of drafts","Hull reports","Anchor record","Machinery repair book"] 简述什么是文献法？ 正常生产中如何切换蒸汽往复泵？ 交-交变频电路的最高输出频率（）。 ["高于电源频率","低于电源频率","等于电源频率","与电源频率无关"] When approaching a fire from win ward, you should shield firefighters from the fire by using（） ["low-velocity fog","high-velocity fog","a straight stream of water","foam spray"] 如何应对客户“对门的客户能订××烟，我为什么订不到”的问题？