单项选择题 If a line at right angles to the axis rotates about that axis and, at the same time, moves parallel to the axis, it will generate （）.

单项选择题 When a point rotates about an axis and, at the same time, moves parallel to that axis, it describes （）.

单项选择题 An emergency bilge pumping system is provided and should be （） of the main bilge pumping system, according to the SOLAS 74 Convention.