单项选择题
A.x+y+z=0 B.x+y+z=1 C.x+y+z=2 D.x+y+z=3
A.2x+4y+z=11 B.-2x-4y+z=-1 C.2x-4y-z=-15 D.2x-4y+z=-5
A.(x-1)/1=(y-1)/1=(z-1)/-1 B.(x-1)/1=(y-1)/1=(z-1)/-2 C.(x-1)/1=(y-1)/-1=(z-1)/-2 D.x+y-z=1