Point: complete square formula. Special topic: calculation problems. Analysis: First, the original formula is deformed to get x2+z2+2xz-4xy+4y2-4yz=0, and then (x+z-2y)2=0, and then the problem is solved. Solution: solution: ∵ (x-z).

∴x2+z2-2xz-4xy+4xz+4y2-4yz=0，

∴x2+z2+2xz-4xy+4y2-4yz=0，

∴(x+z-2y)2=0，

∴z+x-2y=0.

So choose D. Comments: This question examines the application of the complete square formula. The key to solving the problem lies in mastering: x2+z2+2xz-4xy+4y2-4yz = (x+z-2y) 2.