A cone would fit the given description
cone; circle is the base
A cone
the base of a cylinder is a circle.
A circle.
Circle
A circle.
A cylinder is a tube with a base of a circle. A hexagon is a figure with a six sided base.
A cone.
The answer will depend on the figure. A circle or sphere, for example, has a different formula for whatever it is that you want to calculate.
It is a circle, so use the formula "pie r squared" to figure it out
A circle could be, and I think that an ellipse also could be.
It is a sphere.