The sphere. All the others are prisms.
The answer is option c.
That is, the wrong step in step 6. It was written that the center of the circunference is the point (2.1). However, the general equation of a circumference is:
(X- (a)) ^ 2 + (Y- (b)) ^ 2 = r ^ 2
Where the point (a, b) is the center of the circle.
So for this case the point for the center is: (-2, -1)
C=11.27π feet
Diameter=11.27 feet. Hope it help!