A.51B.41C.31D.21
A.Δ/Δ-Y,Δ/Y-ΔB.Y/Δ-Y,Δ/Δ-YC.Y/Δ-Y,Y/Δ-YD.Y/Y-Y,Δ/Δ-Δ
A.與行走軌平行敷設B.垂直行走軌敷設C.相交某一個角度敷設D.前三項都可以