A.23.0N/mm2 B.24.1N/mm2 C.24.9N/mm2 D.30.0N/mm2
A.20d且不小于300mm B.30d且不小于400mm C.35d且不小于500mm D.40d且不小于600mm
A.不宜小于1% B.不宜大于1% C.不宜小于4% D.不宜大于4%