单项选择题
A.ahead direction B.astern direction C.right-handed D.left-handed
The pitch ratio of a propeller is the mean pitch divide...
单项选择题The pitch ratio of a propeller is the mean pitch divided by （）.
A.the propeller diameter B.the propeller radius C.the pitch angle D.the length of helix
If a line at right angles to the axis rotates about tha...
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 （）.
A.a helix B.a helicoidal C.a curve D.a cone
When a point rotates about an axis and, at the same tim...
单项选择题When a point rotates about an axis and, at the same time, moves parallel to that axis, it describes （）.
A.a line B.a circle C.a helix D.an epllicate
