当m-n=-2时,原式=m2-2mn+n22=(m-n)22=(-2)22=2
—Did you have a good weekend?
—________. We enjoyed ourselves very much in the amusement park.[ ]
A. Of course
B. Not bad
C. I'm not sure
D. I hope so
产生波形转换的必要条件是必须有斜入射。