If points `Aa n dB` are (1, 0) and (0, 1), respectively, and point `C` is on the circle `x^2+y^2=1` , then the locus of the orthocentre of triangle `A B C` is `x^2+y^2=4` `x^2+y^2-x-y=0` `x^2+y^2-2x-2y+1=0` `x^2+y^2+2x-2y+1=0`