单项选择题
A.Cranes are more difficult to secure for sea
B.The spotting area of the conventional gear is larger
C.A crane operator requires more training than the winch operator of a yard and stay rig
D.The yard and stay rig is more flexible in its ability to handle a wider variety of cargoes
单项选择题 Which part provides for transverse control and positioning of a boom in a conventional yard and stay system（）.
单项选择题 Which part of a conventional cargo gear rig provides for vertical control and positioning of a boom（）.
单项选择题 Which operation may cause the pressure in an inert tank to fall below the prescribed limits（）.