Excellent solutions to this problem were sent in by William from All Saints, Carshalton and Ruth from Swanbourne House School.
William says that the black circle could
be a sphere, hemisphere, cylinder or cone.
Ruth explains that the square could be a
cube, a cuboid on its end or a square-based pyramid.
The triangle could be a triangular prism,
tetrahedron, one side of any shaped pyramid or a cone according to
William.
Finally, Ruth says that the rectangle could
be any kind of prism, a cylinder or a cuboid. William also suggests
it could be a rectangular based pyramid.
Jonathan from King David High School wrote in with some suggestions of what items could make the shadows:
The circular shape could be an enlarged smarties tube from the
side.
The square shape could be the side view of a die.
The triangular shape could be a view of a tolberone box.
The rectangular shape could be a view of a biscuit box.
This is another way to look at the problem - thank you Jonathan.