曲面z=1-x2-y2在点(1/2 1/2 1/2)处的切平面方程是:A.x+y+z-3/2=0

曲面z=1-x2-y2在点(1/2，1/2，1/2)处的切平面方程是:

A.x+y+z-3/2=0

B.x-y-z+3/2=0

C.x-y+z-3/2=0

D.x-y+z+3/2=0