This question checks whether you can picture what shape appears where two solid cubes cut into each other. It helps to think about what happens right at the boundary where the two solids meet, since that boundary is exactly what decides the shape of the intersection the options describe.
Only the cube option describes something that can never be the shape of the overlap between two cubes, since triangles and rectangles are both ordinary results of one cube cutting into another at an angle, while a cube shaped overlap would need the two solids to stop being two separate cubes.
Let's summarize:
So the shape that the intersection of two cubes cannot be is a cube, option (A).