2x+y=m- 1，(2)

(1)-(2): x+y=2, substitute (2): x+2=m- 1, x=m-3,

Then y = 2-x = 2-(m-3) = 5-m.

x-y=m-3-(5-m)=2m-8=2(m-4)

When m> is at four o'clock, M-4 > 0，x-y & gt； 0，x & gty

A: m> IV