Answer:
1. Triangle or trapezoid.
2. A line
3. Circular
4. Triangular.
Step-by-step explanation:
1. The cross-section of a cone that is perpendicular to the base either of a shape of a triangle or a trapezoidal shape.
If we make the cross-section along the diameter of the base circle then the cross-section will be a triangle and otherwise, it will be of trapezoidal shape.
2. The cross-section of a rectangle that is perpendicular to the base is line only because a rectangle is a two-dimensional shape and if we cut it perpendicularly to the base it will give a line.
3. The cross-section of a cylinder that is parallel to the base is a circle only.
Because the shape of a cylinder is constantly circular along the vertical axis.
4. The cross-section of a triangular prism that is parallel to the base is a triangle only.
Because the shape of a triangular prism is constantly triangular along the vertical axis. (Answer)