下列哪一个不是立体图形的展开图？

1. Analyse Net (1)

Net (1) consists of two squares and three triangles. When folded, the two squares form the base and one side of a triangular prism, and the triangles form the two triangular bases and the remaining rectangular side (if the triangles are right-angled and combine appropriately, or it forms a specific polyhedron). It can fold into a solid (a triangular prism).

2. Analyse Net (2)

Net (2) has four rectangles in a row and two squares on opposite sides. This is the standard net of a cuboid (rectangular prism).

3. Analyse Net (3)

Net (3) consists of 5 squares. A closed solid made entirely of squares is a cube, which requires 6 squares. Since it only has 5 squares, it cannot form a closed solid (it would be an open box). Therefore, it is not a net of a solid.

4. Analyse Net (4)

Net (4) consists of three rectangles and two triangles. This is the standard net of a triangular prism.