单项选择题
Many sheath-screw davits have markings to indicate the maximum angle to which they should be cranked out. If the angle is exceeded，the davit（）.
A.may jam against the stops B.will not automatically position the boat at the embarkation station C.screw may come out of the sheath D.will chafe against the falls and may cause their failure
单项选择题 Maintaining the close tolerances in diesel fuel pumps and injectors requires the use of（）.
单项选择题 Lubricating oil should be changed on a heavy duty diesel engine when（）.
单项选择题 If your propeller is racing in rough weather，you should（）.
