单项选择题 A vessel puts into the port of Kobe，Japan to discharge cargo. While awaiting completion of the cargo operation，the vessel contracts with a local shipyard to have the hull chipped，scaled，and painted. How is the cost of this maintenance handled with the Collector of Customs?（）

单项选择题 A vessel is equipped with cross-connected deep tanks. In which situation should the cross-connection valve be closed? （）

单项选择题 A sling psychrometer is a(n)（）.