x^2-5x+6-m=0

When m=0, ① Right. M≠0, error. So the conclusion is wrong.

(-5)^2-4(6-m)〉0

M >- 1/4, so ② the conclusion is correct.

y =(x-x’)(x-x”)+m

=x^2-5x+6-m+m

=(x-2)(x-3)

Through x, so y=0.

X'=2，x"=3。

Therefore, the conclusion is correct.

Choose C.