单项选择题
A.a’’(x,y,0) B.a’’(x,0,z) C.a’’(0,y,0) D.a’’(0,y,z)
A.a’(x,y,0) B.a’(x,0,z) C.a’(0,y,0) D.a’(0,y,z)
A.a(x,y,0) B.a(x,0,z) C.a(0,y,0) D.a(0,y,z)