单项选择题
A.不应小于4跨,且不应小于6m B.不应小于3跨,且不应小于4.5m C.不应小于3跨,且不应小于5m D.不应大于4跨,且不应大于6m
A.300mm B.350mm C.400mm D.450mm
A.等间距设臵,间距不大于400mm B.等间距设臵,间距不大于300mm C.等间距设臵,间距不大于500mm D.间距不大于400mm