Answer
Rectangular prism
Explanation
The base of a pentagonal prism is a pentagon. Since there is no pentagon in the net, then it cannot be a pentagonal prism.
The net of a rectangular prism has five faces, four of them triangles. The net in the diagram has 6 faces and none of them is a triangle, then it cannot be a rectangular pyramid.
The net of a cube is composed of 6 squares. The net in the diagram is composed of at least four rectangles, then it cannot be a cube.
In conclusion, the net in the diagram folds to form a rectangular prism