单项选择题 Prior to backloading portable tanks or drums onto an offshore supply vessel，check that each tank is（）.

单项选择题 Large quantities of uncovered pig iron or billets should not be carried in the upper-tween decks because（）.

单项选择题 It’s（）to stow optional cargo in the lower hold．You’d better give it block stowage in the tweendecks，then it can be easily discharged either at Shanghai，or Dalian or Tianjin.