A.前后對(duì)稱(chēng) B.左右對(duì)稱(chēng) C.上下對(duì)稱(chēng)
A.下端;上端螺栓 B.上端螺栓;下端螺栓 C.上端螺栓;下端 D.下端;上端
A.20±5mm B.25±5mm C.30±5mm D.35±5mm