单项选择题
A.rigging a back stay
B.raising the boom
C.increasing the mechanical advantage of the cargo purchase
D.taking all slack out of the preventer
单项选择题 Sometimes the contract（）that the lump sum freight must be paid in advance and will not be returnable even if the vessel and／or her cargo are lost.
单项选择题 Securing cargo by running timbers from an upper support down to the cargo，either vertically or at an angle，is called（）.
单项选择题 Roll-on／roll-off ships are equipped with（）.