单项选择题 A conscious victim who has suffered a blow to the head has symptoms that indicate the possibility of concussion. If the patient feels no indication of neck or spine injury，recommended treatment would include（）.

单项选择题 A common class of wire rope used for mooring is the 6x19 class. What does the 6 represent?（）

单项选择题 A CO2 extinguisher on a ship which has lost 10% of its charge must be（）.