If the endpoints of the diameter of a circle are (6, 3) and (2, 1), what is the standard form equation of the circle? a) (x + 4)2 + (y + 2)2 = 5 b) (x − 4)2 + (y − 2)2 = 5 c) (x + 4)2 + (y + 2)2 = 5 d) (x − 4)2 + (y − 2)2 = 5