Rectangle
a rectangle.
A square.
circle just did it on apex
No, a prism has flat sides. Triangular prisms are very common, but any polygon can be the cross section of a prism.
It is a rectangle.
The cross section of cylinder along its length (parallel to the axis of symmetry has the shape of a rectangle.
You cannot have a 2d cylinder. The 2d cross section will depend on the plane of the cross section.
A square.
a circle
Rectangle
a rectangle.
A square.
If the cylinder is standing on its flat face, the horizontal cross section is a circle. Otherwise, it is a line or a rectangle.
An ellipse or a rectangle, depending on how you cut it.
It will be a rectangle
A cylinder is a three dimensional shape with a uniform circular cross section and a finite length.