Question

if a circle is tangent to both the x- axis and y- axis and has a radius of 1, then its equation is
(a) (x-1)^2 + (y + 1)^2 =1
(b) x^2 + y ^2 =1
(c) x^2 + (y + 1)^2 =1
(d) (x +1)^2 + y^2 =1
(e) (x - 1)^2 + y^2 =1