A circle is defined by the equation x²+y²-x-2y- 11/4 =0. What are the coordinates for the center of the circle and the length of the radius?
A. (- 1/2 ,-1), 4 units
B. (- 1/2 , -1), 2 units
C. (1/2 , 1), 4 units
D. (1/2 , 1) , 2 units
E. (1, 1), 2 units