The circle below is centered at the point (3, 1) and has a radius of length 2. What is its equation?
10
A. (x-1)2 + (y - 3)2 = 4
B. (x + 1)2 + (y + 3)2 = 2
C. (x+3)2 + (x + 1)2 = 4
O D. (x-3)2 + (x - 1)2 = 2²