A:(x+1)2+(y+1)2=2
B:(x+1)2+(y+1)2=4
C:(x-1)2+(y+1)2=2
D:(x-1)2+(y+1)2=4
计算(a+1)(a﹣1)的结果是____ .
用开水烫一下番茄,会在其表面撕下一层皮,着层皮属于( )