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答案：D
解析：
Choice D is correct.
The equation for a circle with a center at (h,k) and a radius of r is:
(x-h)^2+(y-k)^2=r^2
The length of the radius is half of the length of the diameter.
1/2*18 =9
Filling in the coordinates of the center and the length of the radius of this circle results in the equation:
(x-1)^2+(y-(-6))^2=9^2
In standard form, the equation of this circle is: (x-1)^2+(y+6)^2=81
