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答案：C
解析：
Segment line C D is a radius of the large semicircle, and it is also a diameter of the shaded circle, so the radius of the large semicircle is equal to twice the radius of the shaded circle. Let r be the radius of the shaded circle. Then 2*r is the radius of the large semicircle, and so the area of the semicircle is (pi*(2*r)^2)/2 = (4*pi*r^2)/2 = 2*pi*r^2. This area is given as 24, and so the area of the shaded circle is (pi*r^2) = (2*pi*r^2)/2 = 24/2 = 12.
