Answer:
A circle.
Step-by-step explanation:
Ok, any plane has a vector normal to it.
Then the plane that cuts the sphere, has a normal vector.
If we draw that normal vector such that it passes through the center of the circle, we can think of this as the "axis" of a cylinder.
Such that when we step on any point of that vector, all the points of the spere that can be reached with a perpendicular line to the vector (like the radius in polar coordinates) are at the same distance of the vector.
Then we can conclude that when we cut a sphere with a plane, the cross-section will be always a circle.
Then the shape that is a representation of the cross-section is a circle.
