If the equation of a circle in general form is x²+y²−2x+6y−6=0, which equation of a circle in standard form does this represent?
a. (x−1)²+(y+3)²=10
b. (x+1)²+(y−3)²=10
c. (x−1)²+(y+3)²=6
d. (x+1)²+(y−3)²=6