因为丨x-1丨+丨y+3丨=0
根据两个非负数的和等于0,则这2个数都为0,即
x-1=0 且 y+3=0
得 x=1,y= - 3
y+(-x)+(-1/2)= -3+(-1)+(-1/2)= - 9 /2
选 A