已知等式x=y,则下列变形正确的是()A.x-1=y+1 B.mx=my C.mx=-my D.5-x=-y+5.已知等式x=y,则下列变形正确的是()A.x-1=y+1 B.mx=my C.mx=-my D.5-x=-y+5.已知等式x=y,则下列变形正确的是()A.x-1=y+1 B.mx=my C.mx=-my D.5-x=-y+5.