单项选择题
A common class of wire rope used for mooring is the 6x19 class. What does the 6 represent?（）
A.Factor of safety B.Number of wires per strand C.Number of strands per wire rope D.Number of wires in the core
单项选择题 A CO2 extinguisher on a ship which has lost 10% of its charge must be（）.
单项选择题 A chart with a scale of 1:80，000 would fall into the category of a（）.
单项选择题 A chart with a natural scale of 1:160，000 is classified as a（）.
