You don't need to know if it's circular/square, that's just there to throw you off. Look at the center of [C] and [D], what do you notice that is different? [D] has a solid line center, and from the Front/End views, we can see that there's some sort of 'hole' going through the object, and the hole opens at the top face of the object. That opening will be represented by solid lines in the Top view since we will be able to see the opening.
[C] shows dotted lines in the middle of the Top view, suggesting the entire top of the object is flat. This cannot be true, as the Front/End views show a hole opening in the middle at the top of the object.